This sounds like he has hygromas and I think you are right the tile floor and him getting up and down and lying on it can be the source of the problem.
You can read about hygromas here
and info on one product to help them heal here
What I did was use a raised dog bed like this to resolve the problem
plus another soft padded bed for the dog to sleep on and over time the dog's leg healed on its own. I have a coolaroo bed in the yard and in the house for the dog.
You can see its kind of a hammock for dogs and its cool as the air circulates under it.
They originate in Australia but you might be able to build a suspended bed similar to this for your dog if you can't buy one.
Hope this helps you!