It could just be a muscle spasm! When i was about 5 months along i woke up to excruciating pain on my left side and it stretched to my lower back and i had it for several hours. It was painful but i took a couple tylenol and used a warm rice bag on it and after an hour or so the pain went away. Try that to see if it works!
No I have laying on my right side or on my back and right now the pain is still on the right side
Have you been laying on your left side? I was having pain like this and it turned out to be uterine irritability. The weight of the baby was making my uterus irritated and so I would get painful contractions sometimes only on one side (the side I was laying on). I went to my doctor and she put me on bedrest. After a few days the pain went away.