Cycle Irregularity

Alright ladies, this is a little tedious, so I apologize. I've always had a super irregular period. I always contributed it to being a competitive swimmer all through high school, stress from multiple shoulder surgeries after that, and then getting on the birth control shot. However, all of these have been a mute point for years and my cycle is still crazy irregular. I've been off the shot for over 3 years now. My cycle ranges from 14 days-38 days. There's absolutely no predicting it. Also, right before my period and up until about day 3-4 of it, I typically gain about 8-10 pounds with no change in diet or working out. I know this is bloating, but it seems a little excessive. When I do eventually get my period, it's always ridiculously heavy. Like I'll go through a super size tampon in 30-45 minutes for 3 days straight. I've also had cramps so bad, I've spent the night on the bathroom floor several times (not every time my period comes, but probably 4 times total). I don't know what else to do. Doctors are mystified and my nurse practitioner just did a ton of blood tests and said all of my hormone levels (except iron levels and my thyroid is slightly low, but not enough to get on synthroid) are normal. She thinks an ultra sound could rule out endometriosis, but that a scope look into my uterus would lead more telling results. For understandable reasons, I'm hesitant to do the scope and I don't think an ultrasound would yield anything that telling. Have any others of you experienced this? Did you ever get an official diagnosis? How did you eventually get your diagnosis (ultrasound, scope, other method)? Please help. I don't know what else to turn to.