Take a sample of your water to the lfs and tell them to write the readings down for you.
Sitting on the bottom can be a sign of a bacterial infection.
Laboured breathing can mean poor water quality, parasites, to bacterial infection.
With out water stats its hard to say what going on it's the first thing you have to investigate.
You say you clean your filter need to explain more, do you touch your sponges in the filter.