your tank is very overstocked with out him as it is. if they are big enough to eat him that makes it even worse, because even if you wait until he is 2", hes going to get ripped to shreads
getting a 50 gallon tub from home depot sounds the best, and you can move some of your fish from the 29 gallon into it until you are allowed to get a bigger tank.
Do you know what kind of cichlid it is? What do you have in your tank right now? About the feeding part, I don't believe that he never got any food on his own. I am guessing that the other fish in the tank bullied him enough that he never came out and got food. Or he might have had some intestinal parisite that cause the small belly. If I where you I would take that fish you just bought back to the store, and have them hold it until you treat your tank for parisites. Sounds like you are new to this hobby or don't know that much. Don't take this the wrong way, but please treat your tank before you buy new fish and add them to that tank. For the fish's sake.
What should i use to treat for parasites? I am not new to this hobby. Been keeping fish for 2 years now and only 4 have died out of all 60 fish that i keep. Also are you serious 50gals for 20 bucks, sounds good.