I've been TTC with my husband for 2 years now. My period is sometimes late but I always have a negative pregnancy test. I live with my sister also and her period always starts after mine. Shes on her period now and mine is 4 days late. I have some lower back pains and when i stand up too fast i cramp mildly in my lower abdomen. My breasts are sore but not unberable. No nausea, no headaches. Period or pregnancy? ?