But the exact smae thing happened to me a few months ago...and it turned out to be a cyst as well! For some reason, they can sometimes cause bleeding. I think I got mine around CD 15.
I think Vitex works for some, and not for others. So I don't have any advice about that, but I do think from what I have seen others say it can cause abornmalities. But again, in others, it seems not to have any detrimental effects.
I wish you the best of luck!