Back Pain Common?

I can feel contractions slightly in my stomach, but it's not super painful at all. So I assume they're nothing serious, they also don't happen very often & im not sure how regular bc I haven't really paid attention. But, starting today, with every contraction, my back starts to hurt SO BAD. Like takes my breath away back pain. I had back problems prior, so pain is normal for me, but should it be so much worse? I haven't had any major changes in discharge, no fluid leaking, and I was at l&d Saturday and was not dilated at all. Am I just worried for no reason? I also just got off work, but usually working doesn't make my back hurt like it did today! I don't want to go to l&d if it's not necessary because I'll be there for 5+ hours & I can't get through to my doctor to ask. Is it normal? I'm 35 weeks btw