How long has this been going on? What kind of doctors have you seen?
A varicocele can be eased by lying down, but finding it with the camera depends on what kind of test they did with the camera. An ultra-sound can find it, but it's not always seen on a cystoscopy.
Do you feel anything weird when you examine the area? You can usually feel a varicocele yourself.
This seems like it would be one of the first things they'd check for, so I'd be surprised if they missed it. It's pretty common, and easily diagnosed.
An inguinal hernia can cause the pain you feel and can also ease when you lie down. An ultrasound can find that, too. You might also have a bulge.
Keep working with your doctor, and if you haven't had an ultrasound of your scrotum or your lower abdomen, ask for that.