What a cute kitty!
Something remarkable about endometriosis is that the extent/severity of disease does not predict the severity of symptoms. The disease-pain relationship continues to baffle researchers and clinicians despite many years trying to unravel this enigma. There are some women with mild disease with very debilitating pain and there are others, like yourself, who have severe endometriosis yet experience few if any symptoms or pain limited to a couple of days a month. Any pain is not ideal, even if it's limited to your period and if you add up all those "pain days" up over a long period of time, the over all impact on your life can be quite significant.
Sometimes women with endometriomas will experience sporadic leakage from one or both endometriomas. The endometrioma contains a chocoloate-like fluid consisting of old blood (hemosiderin) that collects. If this fluid leaks it acts as an irritant (imagine having lemon juice squirted on sensitive tissue) and can cause temporary albeit intense pain before the fluid naturally disperses.
While hormone therapy is a commonly used treatment to manage the symptoms of endometriosis, it's not the only option to deal with this disease. Given your history with cancer, and depending on the type of cancer, it may be considered that certain hormone therapies are unideal in your case or that hormone therapy is best avoided altogether (that's an important discussion to have with your doctor, perhaps in communication with your oncologist). Another thing to bear in mind is that endometriomas do not resolve with hormone therapy (they may shrink a little but studies show that they don't go away and one study even found that birth control therapy made subsequent surgical excision more challenging by contributing to scar tissue formation around the cyst wall). Surgical intervention to carefully free up your ovaries, tubes, and uterus, separating the uterus from the bowel, removing the endometriomas while preserving as much ovarian tissue as possible, and carefully removing disease in other areas (such as the bowel) and peritoneum (the lining of the pelvis which is so commonly involved by endometriosis) may offer an alternative. One thing to bear in mind is that this can be very complex surgery and requires a surgeon considerable skill - someone who takes on these cases regularly and who has had ample opportunity to refine their technique. The surgery also carries risks, just as hormone therapy carries some risks and these risks need to be weighed up against the potential benefits of the treatment. There are several specialist centres in the UK where patients with severe endometriosis can be referred for more specialized care, including the surgery to restore the natural pelvic anatomy and resect/excise areas of endometriosis (separate structures that have fused together and removed the areas of disease). These are the BSGE accredited centres and any GP can refer you (or your current consultant can refer you if you are not already under the care of one of these centres). The care on offer at these centres may also differ, so it's useful seeking the experiences of others to find out which might be the best centre to choose for your treatment. Pursuing care at one of these centres can be very helpful in accessing a full range of options, including advanced surgical care if appropriate.
Here are some questions that may be of help when talking to your doctor about possible surgery: endopaedia.info/treatment.h... The main thing is to go into any treatment decision feeling confident and fully informed of why this treatment is being undertaken and whether it's the right treatment for you. If you don't feel right about the options being offered or suspect other options might be available elsewhere then it's within your right as a patient to seek a 2nd opinion with another specialist.
Best of luck in finding the care most suited to you and try not to feel too overwhelmed. Many of us have been in the same place as you (me included) and it worked out in the end.