Endometriosis is the disease to which you are referring, and it involves endometrial tissue (the tissue that normally lines the uterus and during your cycle generates the blood flow) in abnormal sites. Most often this is somewhere else inside the pelvis or abdomen, but very rarely it can also be outside, and you could have this in your belly button.
Because it is endometrial tissue, like the tissue in your uterus, it responds to the hormonal changes of your cycle, and when you bleed during your cycle, this tissue as well could produce blood. So you may have endometriosis, and that tissue in your belly button may be endometrial tissue, and that is why it would produce blood during your cycle.
You need to see a physician, probably your gynecologist again. Endometriosis can become problematic if not treated properly, as the endometrial tissue can show up elsewhere in the pelvis and abdomen and cause problems there. It sounds like that it is more of a nuisance than anything else, and so your gyn might provide treatment for that.
I hope this answers your question. Take care.
Below is a link you might find helpful for more information:
http://www.ivf.com/endoassn.html
Edited by jcfay on May 18 2006 at 11:21 AM
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