I recently got a FRT. He is not quite right. He cannot keep himself from floating to the top of the tank. He also does not swallow food just bites it and spits it out.
My guess is that it has a respiratory infection. How warm is the water in the tank? You are probably going to want to raise it into the mid to high 80's. I would also take it to the vet ASAP.
it sounds like a gastrointestinal problem. it is can lead to kidney failure and starvation so it needs to be looked at. they need to remove air from the stomach and intestines and he should be fine but sometimes it can come back again.
good luck and I hope that your turtle does alright.