Ovarian cyst, ectopic, something else?

What does an ovarian cyst feel like?  What causes them?  How does it differ from your copus luteum?  I'm having some minor, kinda annoying pain on the left, about 2 inches from my pubic line. I'm only 5 weeks.  At first I thought ectopic, but I don't really have any other symptoms (except for the side pain). My OB suspects possible endo and I know endo can increase your risks for ectopic, so I'm scared.  My HPTs are getting darker which seems like a good sign, but I know that's not necessarily indicative of a viable pregnancy.