Betta sick?!?

Soooo my poor betta fish is sick i think. i had to transport him from my school to my home (it was about an hour long drive) and since then he just hasn't been himself. it might be the water here. he sits at the bottom with his face in the rocks (like...buried underneath the rocks) and wont move at ALL. he'll come up for air, and then drift back down. he hasnt eaten in days (i think he stopped eating a couple days before the trip). i give him a bettafix remedy thing (trying to keep fin rot at bay) and pellets (although he doesnt eat them). help! please! would a water purifier work? or can i used distilled water? i really dont know whats wrong with him. i dont think hes constipated...i fed him half a pea before he stopped eating..maybe that was bad? i read it helped constipation, and before that he had been floating at the top uncontrollably.