I am on my period and having pain on the left side of my uterus. very sharp pain.

Probably nothing: I would, however, do a pregnancy test and repeat the pregnancy test in about a week to make sure that a window period hasn't missed. The brain-ovary-uterus axis is quite sensitive to a lot of things (e.g. Stress, weight changes, diet changes, etc...). Any one of these things, including a pregnancy, can alter the normal cycle and sometimes cause such symptoms.