I’m so worried

Yesterday I volunteered at a food pantry and was helping move some boxes of food around. I picked up a pretty heavy box of meat twice and moved it. Later that night I noticed my back hurt a little, and then overnight my symptoms basically disappeared. I’ve had sore nipples for my entire pregnancy and they don’t hurt anymore. Also my lower back is hurting a bit today. Did I cause myself to miscarry? I’m so worried.