Im on my period and had a large blood chunk that was atleast a size of a nickel?

This happens to me as well, do you have a regular cycle? If not, go to the gynecologist and ask them to check for PCOS- Poly Cystic Ovarian Syndrome.

Relax: it is not scary, in fact most girls have it and don't even know it.

The bloom chunk is just old blood cells that haven't been released; its normal. :D