Just to make sure, id see if it is a sporadic nerve thing happening. I'm having small trouble with my sporadic nerve and I'm only ten weeks :/
If you use a heating pad wrap it in a towel and don't put it up go high. And don't take really hot baths as both can raise your body temperature which is bad for the baby. But both of those are safe still. I noticed if I sleep sitting up my back doesn't hurt as bad.
You can try a heating pad, massage, warm shower or bath. I'm sure there are more options, but those are just the ones I just thought of. Good luck!
Any advice on how to relieve the pain a little??