I'm sorry you had a miscarriage. :( I didn't think fluid in the uterus was generally concerning. Also, it can make the lining appear thicker than it is. How thick was your lining and at what point in your cycle was the u/s done? It's best to have one done 1 or 2 days after your period ends when your lining should be thinnest. You don't want to needlessly undergo a D&C as they can cause Asherman's Syndrome.
Most cysts go away on their own within a few months. Are you sure the 5.5cm cyst is the same one that was 3.5cm 7 years ago? Since it's fluid filled, it is probably a simple cyst as your doctor said and should resolve on its own. Surgery has risks and many women lose their ovary versus just the cyst. Removal of even one ovary has been shown to increase risk for health problems such as dementia and cognitive impairment. It can also impair fertility.
Women who do not have a genetic predisposition for ovarian cancer (OC) have a very low risk of getting OC. Your doctor's correct in that it doesn't make sense to do the CA-125 test. It has too many false positives as well as false negatives so is not useful in diagnosing OC.
Pain from cysts can vary so much from one woman to another but, yes, your right side pain could be from the cyst. But since you also have it in your hip, leg, neck and shoulder, it could be a pinched nerve.
I know tumor sounds ominous but it merely means an abnormal growth, benign or malignant. Most ovarian cysts and tumors are benign. Hopefully, your doctor has good cystectomy skills so that he/she can remove just the cyst... certainly worth discussing before signing the surgical consent form.
I hope surgery goes well! Please post back afterwards.
Another thing to consider... As far as possible endometriosis (endo), have you had symptoms of endo prior to this recent right side pain? Endo symptoms typically present well before your age. Did you by any chance have a c-section that could explain endo being a possibility? As far as exploratory surgery, tissue must be sent to pathology to definitively diagnose endo.
Hope this helps!
So glad to hear your ovary was saved! The gas they pump you up with can cause excruciating shoulder and upper body pain. As far as the heart palps, that could be from (what should be) temporary hormonal upset or the drugs they gave you for surgery. Hoping these post-op effects don't last long and you'll soon be back to normal.