I recently just had my period, and about two days into it I discovered this large lump of flesh which I am aware is not a clot.
I've looked it up on the internet but most of the results keep coming back with people saying it is something to do with a miscarriage and their uterus lining. I am 17, so I am not yet sexually active, therefore I know for certain it isn't anything to do with pregnancy or a miscarriage.
I use tampons, so perhaps it was just my hymen breaking? I am unsure, seeing how I have been told it bleeds when it breaks (though there was no pain) and I was in the middle of my period anyway.
I have done a lot of heavy physical activity in the past (8 years of martial arts). Nothing like this has ever happened to me before, and I was just wondering if anyone could tell me what it was.

Many thanks.
xoxox