I might also add that he needs to be seen based upon symptoms. We cannot assume he is acting different because he is new to your home. If you suspect he has some discomfort only a thorough exam by a vet and possibly xrays will tell you if there is an issue going on. Could be hips, could be knees...could be back....could be no problem at all. Best to let the vet determine that.
As for allergies, usually the first thing I would think of is fleas...did he have any when you got him? Then next thing to look at is environmental. The blood test for environmenatl allergies is reliable. The one for food allergies is not. That would require a food elimination diet. Most pups have environmental allergies and that is easy to find out...but the test is a bit costly. There are meds that can be given for allergies, but personally, I would want to know first what it is.
Bottom line: Make a vet appointment !
