Extreme back pain especially on the lower right side since 2months, only while taking a turn on lying down, ok while lying still, is this muscular ?

Needs evaluation: Sounds like this pain is persistent and debilitating, making it concerning for something more than muscle strain. Should see a physician about work-up and management, which can be conservative to start. If associated weakness or bowel/bladder symptoms, should urgently seek work-up and treatment.

Sacroiliac Pain: Extreme is certainly worrisome. If you find you have pain in the buttock region that does not radiate, this could be si pain, which is not serious. Seems to worsen with any movement (sit, stand, lying), but better when still. Thyroid disease also makes stress fracture a consideration. If this has continued 2 months without improvement, see a doc. May need MRI and/or bone scan to diagnose.