Throbbing Lower Back Pain. Not Pregnant. Could It Be A Nerve Pain Or Kidney Pain? Have Hypothyroidism

For the last month I ve had a throbbing lower back pain . Seems like it could ve been kidney-related, but I recently had a general checkup in January and blood work done and my kidneys are fine. I also haven t had my period for about 4 months now. I m normally irregular, but have never had this long a time in between periods. I took two pregnancy tests and I m not pregnant. My OBGYN had told me last year that I had a terratoma (large cyst) and that it may just be nerve pain from that, but never pursued it and the pain went away and returned about a month ago. Since then, it s been far more severe and painful than ever before. Other than this, I don t suffer from anything else except hypothyroidism caused by Hashimotos Disease that I take levothyroxide for. Any thoughts?