Cramps in my lower back. Period different?

Im havin strong cramps in my lower back..real heavy cramps.! Everytime i burp i feel heartburn. Feels like throwup in my throat. Nipples kinda sore. Period is only wen i pee. N wipe..could i b pregnant?? Why am i bleeding?? Is this my period??. Its not real heavy, i can wear a panty liner n go. Im confused cus the cramps are low in my back n sides.