I have an 11 year old Maine Coon named Scoobie. In the last week his stomach has swelled so much he looks pregnant. He acts hungry at times and not at others. Purs when loved. I cannot afford a vet right now either. Do to his age I am so scared of what may be wrong. It was like in a few days his stomach swelled. What may be causing this?

What comes to mind is either fluid retention for some reason, perhaps cardiac in nature or FIP.
Another thing that comes to mind is a tumor.
These are only guesses and it could be something else entirely.
An exam shouldn't break the bank, however testing and diagnostics may get expensive.
I would take him in for an initial exam and go from there.