Other forms include Epsom Salt--Mg sulfate. Some prefer the more subtle effect of a foot bath.
If you take too much Mg you can get too much gas and loose stools.
Mg glycinate is probably one of the better forms for a calming effect. The glycine in it is also useful to us.
If GABA did nothing for you I'd consider a need for more liver support. This is very complex so you have lots of homework : ( Learn about how the body breaksdown natural and other chemicals that amp us up--adrenaline, phenols, etc.
You might need a more careful diet to lighten the load on your liver.
If your hair or other test reports very low lithium you might like a couple mg of it from Li orotate or similar. It won't be a cure-all but might be a puzzle piece.