Exercise

Just now I tried to exercise with my period on and I couldn't. I was out of breath fast and I couldn't even finished the routine because I was so tired. Mind you I just worked a 9 hour day, but everyday last week I worked out after work and I was fine. Is it because I have a flow right now or because my mental is not cooperating with my body and that's what's making me tired? Thoughts ? Opinions? Advice plz ?