sometimes when you just buy betta they might don't eat...it happened a lot. But with your betta i am confused. I think you wrote in another post he was eating before?
Another thing if he is active like you wrote he looks happy then he probably adjusting to the new environment. I also remember your previous post about temperature. What temperature he is now?
And i got confused because i think may be i am wrong you wrote in another post he is a little lethargic stay at the bottom most of the time or hanging on the top?
If he is like that lethargic then something is wrong.
If he is active , swimming around like normal betta then he just adjusting to the new environment. I know you transfer him from i think one gall to 2.5 gall.
You wrote that you do 2 water changes a week?
Also when you do water changes especially when you do 100% do you acclimate him?