Hello, Are you wondering if your pain could be caused by a thyroid condition? I did not have that as a symptom for my hypothyroidism, rather the opposite (light to skipped flow), but I'm also perimenopausal, so it is not clear cut. However, my last few regular periods before I virtually stopped having them was similar to yours in that I experienced significant back labor type pain. Ibuprofen can help with that. Have you talked with your gyno lately? Might be worth ruling in/out reasons that are causing your symptoms. Good luck!
I would see your physician, or go to a clinic.