SounRAB like it might be sciatica pain that you have. Have you had this in the past? It's NOOOOO fun to have. I started having that pain while pregnant with my 2nd child 3 years ago and it has continued. I was finally referred to a neurologist and she prescribed my gabapentin and it has helped quite a bit.
There are also certain stretches that can help alleviate (temporarily) the pain, and also some yoga poses that can help. Have you been to the doc about it yet? You may have a pinched nerve or something.
Sorry you have this, I completely sympathize iwth you.