hip locks and grinds then cracks when pulled out

I have been dealing with chronic lower back pain for years and also my hips locks on my all the time and grinds when i jerk it back it makes a big cracking sound and hurts when it cracks, burning sensation down the butt and left leg. had steriod injections in back and worked for awhile went to p.t. and had to stop due to the exercises made my hips lock and crack from the exercises. went to an orthopedic doctor did an x-ray of hips everything normal. had an mri of hips everything fine except a little fluid on hips. had an hip injection on left hip and the pain left for a little bit but is back to doing the same thing. doctor seems confused about all this. is this normal for a hip to lock and like catch and have to jerk it back and then it make a really loud cracking noise? thank you for any advice.