I generally feel bad during the first days of my period, I'm in a bad mood, sometimes tearful for no apparent reason, my whole body and especially my back and abdomen hurt and I have cramps. My always low blood pressure drops even lower and sometimes makes me feel dizzy.
I still try to exercise because really helps with the mood and cramps, but I don't push myself if I don't feel like it. Using the mooncup really helps with all kinds of exercise during my period.
As a teenager I was very unhappy with these monthly problems, and even took the pill for some years to avoid it. It got better since I treat this week as a time to take it easy and relax. I try to see it a bit like an ancient ritual - sounds stupid but makes me feel a bit better about it