When I play some songs my thumb is lower than the middle of the guitar and its not pointing up its pointing to the side.
You should try to learn how to keep your thumb behind the neck in the area between your four fingers. This means not gluing your thumb to a particular spot and just moving your fingers around but lifting your thumb from the neck and repositioning your whole hand in relation to the fingerboard position. A lot of beginners squeeze the neck between their thumb and fingers and it's not necessary to use a lot of force. This will also help increase you range as you're not pinned to spot on the neck.
Moving on.....
I backwards i use my thumb a lot so i been trying to get use to doing thumb barre chords O_o

Guitar : Fender CIJ Mustang and a Telecaster
Amp : 76 fender champ
Pedals : BBE green screamer, Big muff, Ibanez LU20 Pedal Tuner, boss loop pedal