Irregular Period

Last month my period came over a week late. And now my period came 8 days early and is very heavy. I have had both protected and unprotected sex both months. Could this be a miscarriage? Or could it just be from stress? I have lost weight from the stress of starting college and my boyfriend joining the military. Could my body just be evening itself out from the late period last month? I've also been feeling nauseous and had headaches but that could also be from stress and the change in altitude.