I ate whatever i wanted and weighted 135 in october. started to watch a little and was about 132 in november. got gerd and changed diet now i weigh 123. is all this weigh from diet or is something else wrong with me?

I am not sure how your diet adjustment has been. If you only stop the foods which exacerbates the GERD symptoms but not actually cut down on the total calorie intake, losing more than 5% of body weight in 6 months could be significant. If GERD was diagnosed by upper endoscopy and you have no other symptoms you should be safe. However, if endoscopy wasn't done then it is time for a follow-up visit.

It is not clear from your question whether the amount of weight that you have lost was expected or whether this was unexpected weight loss. If you lost more weight than you would have anticipated, you may need to speak to your doctor or a Gastronenterologist for evaluation. Good luck.