I have a friend who is very slim and her she has struggled with multiple ovarian
cysts. You can see them on her like you are describing. So, my bet is that it is a cyst. Most
cysts turn out to be benign and go away on their own over time. But, the ultrasound is the best next step to see what is happening. I don't think you would see an ectopic prenancy like that. Your fallopian tube would have ruptured with an ectopic before you would be able to see it visibly.