Chronic SI and hip joint pain with popping/cracking. Normal XRay and MRI. (HO hip dysplasia as infant) Pain is getting worse. What can cause this?

Hip Pain. Hip and SI joint pain have a great deal of overlap. There are many things that can cause these symptoms, such as bone deformities, muscle and ligament injuries, as well as bursal abnormalities. If there is a history of developmental hip problems, further evaluation would be beneficial to make sure there is no lasting effects.
OSTEOARTHRITIS. Children who have hip dysplasia commonly develop osteoarthritis in the hips at an early age. This needs to be treated with medicine and/or with physical therapy. Despite aggressive medical management, young adults with your history may ultimate require total hip replacements. You need to see you physician to set up treatment.
Normal MRI. If indeed a recent MRi was normal the cause of the pain might be in the lower spine or ischial tuberosity, causing what we call referred pain.