A lap is the way to go dear. And don't worry an u/s would not detect endo they really need the lap to definately say it's endo. I know it sounds flipant but laps are not that big an operation - I've had seven and on all but one occassion it ws day surgery and apart from having some period type pain for a few days it was fine. Although Im aware that I'm at ease with hospitals and surgeries (after many years of same) and that you and other ppl may not be.
I wish you all the very best for your lap and be sure to let us know how you go. It truly is a wonderful way to get some answers and so the doctor can advise you in the right direction as far as TTC goes.

BTW if it is endo, unless it is treated you may continue to have difficulties but after the endo is removed most doctors suggest that your chances of conceiving are greatly increased. So there's another good reason to go get it done ASAP.

Again good luck,
Cindy