Jeepy, I have been following this thread with interest, but pardon my igonorance: when you say you were "spayed" long ago, that doesn't mean hysterectomy?
(it couldn't because then you would not be menstruating?)

I do hope you find something that works for you. This probably isn't much help, but when I took BC pills (for birth control) I had nonstop breakthrough bleeding, but kept changing brands until it stopped.