It is difficult to see our furbabes get on in age. However, you already have a gut feeling of what is happening. Follow them.
I know you do not want to hear the staple 'we are not vets' but we are not. I truly believe your best answer will come from a professional which we are not. Sorry to say this, but I think a vet visit is in order.
Best to you and your angel. This is the time when a beloved pet needs us the most.