it could be gas pains or round ligament pains too. I know sometime I get both of these so bad I'm in tears just trying to move. My dr also told me that sometimes your pubic bone gets inflamed and that causes some awful pain as well.
I'm sorry you're going though this...pain during pregnancy is no fun.
Good news is that during pregnancy your organs tend to move up, including your appendix, so that may not be your problem. Many women have lower stomach pain during pregnancy and it could be due to many things. Usually it's just the baby's position. At 27 week, baby is starting to run out of room already!
I do hope you are able to figure out the cause of the pain and rule out anything serious.
The ultrasound will rule out kidney stones which can be common in pregnancy as well. Did the doctor do bloodwork? If so your white cell count would be elevated usually if it was your appendix. I hope that it shows you are alright and the pain goes away soon