Back pain???

So last night around 2am, I woke up to go pee. I don't know if I got up too fast or something but I felt this indescribable back pain once my feet hit the floor. Almost felt like it shot up my spine and spread through my sides. It hurt to move, so much that my legs almost gave up but I was able to get a grip and go to the restroom. Well I woke again at 4am to get my SO's things ready for work and it was gone so I didn't think anything of it. Well silly me, it was back when I woke up at 9am. It's not as bad as it was when it first hit but it is very uncomfortable and I can definitely feel the soreness. I'm currently 35 weeks. Has this happened to anyone else? If so, why would you say this happened? I'm a FTM and would very much love to know more about anyone else's experiences. TIA!