Do Pit Bull's Have A History Of Hip Dysplasia? All Of A Sudden Our Pit Bull Won't Jump On The Bed And Has A Hard Time Walking Up Stairs

HD is one of the issues they are prone to and good breeders should have their dogs hips cleared (OFA, Penn-hip ect.) before breeding as a bare minimum of health testing.
Some of the dogs are being bred for appearance only (I feel soooo bad for those poor deformed things) and not what they are actually supposed to look like (or be as they are one of the most versatile breeds there is and it is being destroyed right along with their skeletal structure and the breed by SO much bad breeding) and this is also causing more painful skeletal defects.
HD can be environmental as well and also can happen due to accelerated growth, excessive muscle or 'bulking' up which is common with Pits and especially too soon not to mention safely, over working and especially during growth stages ect.
You may also be seeing signs of a torn ACL or even a spinal problem or something so you should have your pup checked out. HD would be the first thought though and they are high up in the ranks with even the few breeders that do actually try to make sure they are using good practice and breeding healthy dogs and producing healthy pups.
www.offa.org
www.apbt.info
www.apbt.info