whats wrong with my fish?

can someone please tell me what is wrong with my betta, for the past few weeks he's barely been active even though i'm feeding him regularly and doing constant water checks, i have everything he needs but i don't know what's wrong with him and he was moving before this but for the past 20 minutes he hasn't moved from this one spot, i don't know if he's dead or not but can anyone advise me on what to do for him.