Me again...Still having trouble getting my little guy to eat or even be interested in food.

It has been 2 1/2 weeks and I don't know how much longer he can go. He is very very tiny compared to how he was and barely swims around. I have done everything I know I could do. I got him a new tank, heater, everything! The test strips all come out normal and the temperature is fine. I just don't know what to do anymore and it's really stressing me out. I just want him to be okay it's killing me seeing him suffer!! Please if anyone has tips on what I can do differently I would soo greatly appreciate it.