Hi Sue - I would think that lower back pain is very common. I have had back pain in my lower and upper back on and off through the whole pregnancy. My ob said that sharp pain, and pain in the upper belly are usually nothing to worry about - it is more cramping across the middle that is a concern. If you find it continues, maybe see a physio or osteopath. It is most likely just your body getting used to the uterus expanding. If you are worried, call your Dr though as they will be able to give you some reassurance.