Re: Cancer/Endometriosis? What? Bits of grossness here, sorry. Sick of Pain.
I would request a colonoscopy. Blood in the stool can be due to many things but you need to rule out the more serious causes and put your mind at rest. Depending at what age your father was diagnosed, you should be getting regular colonoscopies .. I believe it is ten years prior to when your relative was diagnosed.
If your mother had ovarian cancer then this is certain a good reason to continue to have regular ultrasounds to keep an eye on your ovaries. Endo will continue to form as long as you are getting estrogen. The pill contains estrogen as well as progesterone and although you may be on a low dose pill perhaps, you may simply be retarding the growth of the endo and not stopping it altogether. I think it is quite reasonable for you to request an ultrasound, especially in light of the pain you are having.
For the pain you should request a strong anti inflammatory like Naproxen. This will help with combatting the prostaglandins that actually cause the pain, rather than masking the pain with pain killers (that may become addictive .. you definitely don't want that). Advil works too but the Naproxen can be taken once a day and Advil has to be taken several times a day. A strong heating pad also works wonders on this type of pain, as do warm baths. Ultimately, the cause of the pain, especially if it is endo, will have to addressed but this may help you to cope in the meantime.
Ask for the tests that you need. I do not think this is unreasonable and neither should your doctors.
I hope everything works out. All the best.