I have been doing a lotof research on the topic lately as I have had irregular periods. It can be quite scary and not having insurance makes it even scarier, so I feel for you and please feel free to ask any follow up questions as I am visiting my doctor next week and can ask your questions as well. Anyhoo, it sounds like, based on the color of your bleeding at time that it could be endometrioma. It is signaled by blood often the color of chocolate or close to it and can cause irregular bleeding.
It could also be that your entire lining is bleeding at different times for some reason.
I am not sure about how important reproductive health is for you at this point, but thought there are no definite connections fom what i've read it is something to check out. how long has this been going on...the irregular periods?
Google endometrioma and jsut read up on it. It could be a phases, but something is causing it.
Good luck.