lower back pain at 4 months?

Sarah
Hey ladies,
Any of you guys having a sore back already? I'm anxious in case this is a "gained too much weight already" thing (although I actually don't know how much I have gained having been away from my house and scales for 3 weeks). Or maybe it's normal? To be fair I've got weird fused vertebrae down the bottom but they haven't bothered me for years... any mommies in the same boat?