It depends on how well the doctor looks around. Sometimes the endo is obvious, other times it's located in hard to see spots. Size doesn't relate to pain however. Small adhesions can cause lots of pain while big ones don't, just because of where it's located.

You should talk with your doctor about surgery. It isn't something to take lightly, but many women find great relief. I personally didn't see a change in pain levels when I had mine in May but just having the confirmation that I did have endo, that it wasn't in my head, has made a world of difference. I had to push my doctors a little for surgery since I'm also young. Don't be afraid to assert what you want.