Back Pain

I shouldn't complain because honestly this pregnancy has been what seems to be a cake walk compared to what I see other people experiencing...I have had virtually no morning sickness, no real complications, and am not stuck on bed rest...but now the pain I have in the middle of my back is HORRIBLE! Truly it hurts constantly and is soooo bad. It has been like this for the past 2 weeks. I can't decide if it is just being pregnant, the baby's placement, the way I am walking, the way I am sleeping, or my job. I think mostly it is my job, and I am not complaining about my job at all.... it is just that I am constantly getting up and down off the floor and when I do sit, I sit in mini sized 1st grade chairs. I think the combination of those elements and the large belly equal mid back pain. I have been coming home every night this week and going straight to taking a hot bath. It definitely seems to help instantly with the pain. The heating pad is another thing that helps if the pain comes back. I am really just trying to avoid taking any pain medicines. We will see how much longer I will be able to hold out. But again, if this is the worst part of the pregnancy process for me, I think I am still one of the lucky ones.