What could this be?

I think those symptoms could occur with endo, fibroids, or ovarian cysts. I don't think there is such a things as uterine cysts? Yes you can have ovarian cysts without having PCOS. Although usually with a cyst it's more common to have really bad pain when the cyst ruptures and then the pain goes away. Fibroids can have a variety of symptoms including heavy bleeding with your period, increased cramps, more frequent urination due to pressure on the bladder, constipation if they're compressing the colon, etc. They should be able to diagnose/rule out fibroids and ovarian cysts with an ultrasound. The HSG will rule out/diagnose fibroids in the uterine cavity. I don't think either test will diagnose endo. I'm pretty sure endo can really only be accurately diagnosed via a laparoscopy.

Hopefully whatever it is is easily treated

I think LisaG said a lot of good stuff. I have had endo since 2006. I had softball sized cysts in my ovaries. The difference between endo cysts and regular ovarian cysts are that the endo cysts are filled with blood and other "matter", they are actually called chocolate cysts sometimes. I can tell you that the pain that you are describing is similar to what I experience...I am NOT saying that you have endo though, there are many possibilities. An ultrasound does not diagnose the endo but can help your doctor narrow down the possibilities by telling you whether or not your cysts have "matter" in them. I have major cramping in my uterus, and pains in my ovaries and rectum. Sometimes the pain would severely escalate before a bowel movement. My pain was so severe that I opted for the laparoscopy. They do it as an "exploratory" surgery and then remove any endo that they find while they are in there. I had the surgery and by the next month I was pregnant! I had a beautiful baby boy. I am actually pregnant again, despite the doctors telling me it would never happen once let along twice! Keep your hopes up and don't draw any conclusions until you know for sure.

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Thanks for the info. I wouldn't say my pain is severe, though. More like moderate, although I have had severe pain in the past. I can go to work still, but maybe once a year or so I get the period from h*ll where I am doubled over crying.

I knew that endo couldn't be diagnosed any other way than laproscopy, but I was thinking that the HSG and ultrasound would help the doctor with a guess. I'm glad to know that the other things can be diagnosed through the HSG and ultrasound, though.

I'm nervous about the HSG. I have it a week from today. I've heard it's not a big deal, but the pamphlet says that I shouldn't drive afterward, so that's what makes me nervous. I am prone to panic attacks when I don't feel well, and I don't want that to happen. I am excited about the increased chance of pregnancy for 3 months afterward, though.

I have another question that is somewhat related. When you say you had softball sized cysts, how do they fit in there? I've always wondered this. Wouldn't your belly stick out, or does everything just get squished in there?

Sorry if that's a weird question.