Concern about advice re: SI joint and L4/5

Following 3 months of hamstring pain in right leg, saw physio. People on the forum thought it might be SI joint/sciatic pain.

I have had 2 physio sessions, and the first worked on mobilising SI joint which involved pressing down in time with my breathing about 6 times, then doing so with a 'twist' to try and unlock it. Two of these sets were performed. After that session the hamstring pain went. But the lower back area was tender and stiff after a day or so, lasting until my next session.

I went back for a second session 4 days later, and the physio worked on trying to ease L4 & 5 which seemed tender, which involved rocking me back and forth on my side, for quite a long time. I now feel my back muscles are in spasm to some degree since then, and painful.

I spoke to the physio today, which is now 5 days post treatment, and asked whether this could be caused by the treatment, but she seems to think it's more a moving of the pain from leg to back. I think it's reacting to the treatment. I feel I should let it settle rather than keep on going at it! Feels inflamed and the anti-inflams and ice/heat help only a bit. Painful to sit, walk, stand. Lying down on side helps.

I'd appreciate any thoughts. Doc has referred me now for MRI scan. My inclincation is to let it settle before further treatment as I don't want to make it worse.