3 days late, cramping no tenderness..?

In October of this year I lost my first pregnancy twins, (Paisley and Delilah.) My husband and I have been trying but since the D&C, I went from haveing a 28 day cycle, to having a cycle that has been anywhere from 28 to 31 days, this month I'm late by three days, ( I'm going by 31 days to be safe.) I'm crampy, but no sore . I had sore from the get go with my first pregnancy, I took a HPT (EPT digital one) this morning ( first thing in the morning.) and got a neg.. could it still be to early to tell? I don't FEEL like my period is coming, normally I'm very PMSy, and I don't feel like : "Oh Aunt Flo's coming to town." I also have cervical mucus (sorry TMI) out the whazoo.. If I could be pregnant, does anyone know of anything I can to do to prevent the same thing that happen with my twins from happening again? I didn't drink or smoke...I thought I did everything by the book....