Lower back pain.. could be from pregnancy?

Has any one ever experienced lowed back pain while pregnant? It just feels really sore, its not a shooting pain. But then I stand up or bend to stretch its really sore like I have been working it out. This has been the last 4 weeks now and it seems to be getting worse. I have taken many home pregnancy tests all negative but I would be 6 weeks if I am. My boobs are finally getting sore but I haven't been feeling sick just dizzy. I also have been eating guacamole everyday the last 3 weeks and I read avocados help with morning sickness so I am wondering now if that's why I haven't felt sick at all. I stopped eating them yesterday so we will see.