M., is that cyst on the left side that you mention on your ovary? Ovarian cysts are very painful. Sometimes they burst, which is REALLY painful, like giving birth! And if they don't burst but just stay there, sometimes they have to be removed. I have had both (actually, I have a small one right now on my left ovary but it doesn't seem to be growing, so it doesn't hurt too much). It's worse for you because you are pregnant.
Ask you doctor more questions about this cyst, because it doesn't seem that they have explained your condition very well to you. Ask what happens as your uterus grows with the pregnancy.