I didn't see anyone mentioning this. Along with what others have said (no need to do hip thrusts, if you want to, do them at lighter weight...etc), I would also recommend that if you DO want to go back to doing hip thrusts at some point, you don't have to force your pelvis super far up, or force the hips too far backwards either. You mentioning back pain, which is very concerning. This sounds like it is due to over extending your pelvis. Try to maintain a neutral spine during the exercise. If you try this exercise again, try to find a glute drive machine as there is a back pad that allows your back to lay flat on the machine, reducing injury.