It's probably your ligaments stretching as your uterus expands. Make sure to ask your doc about it though. Congratulations on your pregnancy!
Sometimes you can have some bowel problems in early pregnancy like constipation that can cause a right or left side pain that comes and goes.
If it doesnt get better i would check with the doc.
Hi I had the same problem at 16 weeks but it gotten so bad that I couldn't sleep so I went to the doctor and found out it was a Urinary Tract Infection so I advise you to check with your doctor just like the other girls said it can be a block bowel or your ligament just stretching.
I actually went to the ER on the suggestion of the on call nurse at my OB for exactly this. I believe I was 13 weeks and a few days. (It ended up being nothing but they wanted me to go to the ER anyway because of my past miscarriages) They thought that it might be an ovarian cyst but they couldn't get a good picture of the ovary with the baby in the way. The doctor I saw also said that along with the ligament pain of your uterus stretching there's a lot of bloating in your colon and pressure from the uterus at this time. Since your descending colon is on your left side it's possible that this is where the pain is coming from.