It is not really common for any dog to have those problems at a young age. How long has this been going on? He should be evaluated by your Vet. It could just be a pull or strain or some spinal or hip issue. Your Vet may want to take X-rays.
No, it is not normal for any dog to have these issues, I would recommend a visit to the vet to have a set of hip x-rays done.
Pit bulls and their mixes are some of the most overbred dogs there are today, and the bad part is that the people who breed them are not looking to improve the breed, they are either looking to have a litter of puppies to sell, or their unneutered or unspayed dog has either impregnated a neighborhood dog or gotten pregnant by a neighborhood dog. Probably half of the litters produced are accidental litters that happened because the people either didn't bother or could not afford to have their dogs spayed, resulting in "oops" litters. Even in the litters that were intentionally bred chances are extremely good that no thought was given to the health of the parent dogs' hips, so it is very likely that many of these dogs will show signs of hip dysplasia as they get older.
As I said, it's best to have your dog x-rayed by your vet so you can either confirm the hips as a problem or eliminate them as a problem and go on to test for and diagnose something else as the cause of your dog's discomfort.