What Causes Cramps During Menstruation?

Ive been having a warm sensation in my lower abdomen where i would usually get menstral cramps that are later accompanied by small cramps any ideas what it is? My period has never been irregular (except when on oral contraceptives) usually lasting for months or disappearing for months and i have painful cramps when on my period.My mom had endometriosis im wondering if this is it? Also im not aure if its related but ive been having short sharp pains on my sides below my ribcage and the other day when i was walking i got a sharp pain in my back and had a short trouble breathing. Is this serious? help !? Thanks in advance . Email: YYYY@YYYY