Trouble running MySQL on OS X 10.9.5

So I ran over a lot of post treating of this specific problem but none of the answer seems to work for my case.

So this is the process :
I installed mysql via homebrew that lead me to this :

Marjorie:~ Mawel$ brew install mysql
==> Downloading https://homebrew.bintray.com/bottles/mysql-5.7.11.mavericks.bottle.tar.gz
Already downloaded: /Library/Caches/Homebrew/mysql-5.7.11.mavericks.bottle.tar.gz
==> Pouring mysql-5.7.11.mavericks.bottle.tar.gz
==> /usr/local/Cellar/mysql/5.7.11/bin/mysqld --initialize-insecure --user=Mawel --basedir=/usr/local/Cellar/mysql/5.7.11 --d
Last 15 lines from /Users/Mawel/Library/Logs/Homebrew/mysql/01.mysqld:
2016-04-03 22:00:14 +0200

/usr/local/Cellar/mysql/5.7.11/bin/mysqld
--initialize-insecure
--user=Mawel
--basedir=/usr/local/Cellar/mysql/5.7.11
--datadir=/usr/local/var/mysql
--tmpdir=/tmp

Warning: The post-install step did not complete successfully
You can try again using `brew postinstall mysql`
==> Caveats
We've installed your MySQL database without a root password. To secure it run:
    mysql_secure_installation

To connect run:
    mysql -uroot

A "/etc/my.cnf" from another install may interfere with a Homebrew-built
server starting up correctly.

To load mysql:
  launchctl load ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
Or, if you don't want/need launchctl, you can just run:
  mysql.server start

I tried mysql.server start

Starting MySQL
. ERROR! The server quit without updating PID file (/usr/local/var/mysql/Marjorie.local.pid).

I looked for the file but the parent folder was empty :

Marjorie:mysql Mawel$ cd /usr/local/var/mysql/
Marjorie:mysql Mawel$ ls -all
total 0
drwxr-xr-x  2 Mawel  admin   68 Apr  3 22:27 .
drwxr-xr-x  5 Mawel  admin  170 Apr  3 22:00 ..

I then saw

Warning: The post-install step did not complete successfully
You can try again using `brew postinstall mysql`

So I run it after giving acces right to it.

Marjorie:etc Mawel$ brew postinstall mysql
==> /usr/local/Cellar/mysql/5.7.11/bin/mysqld --initialize-insecure --user=Mawel --basedir=/usr/local/Cellar/mysql/5.7.11 --d
Last 15 lines from /Users/Mawel/Library/Logs/Homebrew/mysql/01.mysqld:
2016-04-03 22:24:00 +0200

/usr/local/Cellar/mysql/5.7.11/bin/mysqld
--initialize-insecure
--user=Mawel
--basedir=/usr/local/Cellar/mysql/5.7.11
--datadir=/usr/local/var/mysql
--tmpdir=/tmp


READ THIS: https://git.io/brew-troubleshooting
If reporting this issue please do so at (not Homebrew/brew):
  https://github.com/Homebrew/homebrew-core/issues

Still no changement at mysql.server start

Anybody could help me pls I really don't know what to do anymore :/

As a plus : here is my.conf (should I edit it ?)

# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html

[mysqld]

# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M

# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin

# These are commonly set, remove the # and set as required.
# basedir = .....
# datadir = .....
# port = .....
# server_id = .....
# socket = .....

# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

# CUSTOMIZED BY MMVMySQL SCRIPT - JUST GENERIC SETTINGS
# DO NOT TREAT AS GOSPEL

innodb_buffer_pool_size=2G
skip-name_resolve
max-connect-errors=100000
max-connections=500

#
# The MySQL database server configuration file.
#
"my.cnf" [readonly] 170 lines, 4719 characters

Edit

So after klanomath proposition I decided to clean all my mysql file and remove by the same time MAMP and MAMPro since they could be conflicting.

First step :

Marjorie:mysql Mawel$ brew uninstall mysql
Uninstalling /usr/local/Cellar/mysql/5.7.11... (12,817 files, 440.5M)

Then I ran sudo find / -name mysql and decided to clean it all :

/Applications/MAMP/db/mysql
/Applications/MAMP/db/mysql/mysql
/Applications/MAMP/Library/bin/mysql
/Applications/MAMP/Library/lib/perl5/site_perl/5.22.0/darwin-2level/auto/DBD/mysql
/Applications/MAMP/Library/lib/perl5/site_perl/5.22.0/darwin-2level/DBD/mysql
/Applications/MAMP/Library/lib/python2.7/site-packages/mysql
/Applications/MAMP/tmp/mysql
find: ‘/dev/fd/3’: Not a directory
find: File system loop detected; ‘/dev/fd/4’ is part of the same file system loop as ‘/dev/fd’.
find: File system loop detected; ‘/dev/fd/5’ is part of the same file system loop as ‘/dev’.
find: File system loop detected; ‘/dev/fd/6’ is part of the same file system loop as ‘/dev/fd’.
find: ‘/dev/fd/7’: Not a directory
find: ‘/dev/fd/8’: Not a directory
/Library/Application Support/appsolute/MAMP PRO/db/mysql
/Library/Application Support/appsolute/MAMP PRO/db/mysql/mysql
/private/var/mysql
/Users/Mawel/Library/Logs/Homebrew/mysql
/usr/local/var/mysql

I hard cleaned up this and finish with this :

Marjorie:/ Mawel$ sudo find / -name mysql
find: ‘/dev/fd/3’: Not a directory
find: File system loop detected; ‘/dev/fd/4’ is part of the same file system loop as ‘/dev/fd’.
find: File system loop detected; ‘/dev/fd/5’ is part of the same file system loop as ‘/dev’.
find: File system loop detected; ‘/dev/fd/6’ is part of the same file system loop as ‘/dev/fd’.
find: ‘/dev/fd/7’: Not a directory
find: ‘/dev/fd/8’: Not a directory

And finally I ran again brew install mysql

And same problem came up :

Warning: The post-install step did not complete successfully You can
try again using brew postinstall mysql

And same schema again.