First off welcome to the board. I would switch the food if price is an issue try the presidents choice 1st food it is pretty good. Honestly Iams sucks as far as quality goes I think the second ingredient is corn or right near the top and corn is just filler no nutritional value at all. Second I would get a thicker bed Costco online has memory foam dog beds and they are reasonable and really good. I have used them with my Mastiffs. A vet check would be in order big dogs are prone to joint problems and adding glucosamine to the food is a good supplement for joint and bones. Limit the amount of running and jumping he may have pulled a ligament or muscle. Please let us know how your dog is doing
A dog has so many friends because they wag their tails not their tongues.
R.I.P. Buddy 2002-2008 The best Mastiff ever.
Now owned by Clark the Crazy American Bulldog