Someone help me save my possibly dying red tail catfish?

he seems to be sick hes thrown up a couple of times i've seen him once and small pieces of food on the bottom of the tank seems to point to throwing up he used to be very happy always swimming around when i shut the lights of now hes much less active and wont eat and looks like hes starting to give up i think it could be from bad food frozen fish bought from a store possibly feeders and i have fed him night crawlers once to see if he wanted it anyways help me out please ive had him since he was 2 inches hes now ten