Missed Period.. Confused?!

Well today marks 4 days late for my period. Not sure what's happening exactly. I took 2 pregnancy tests and both turned out Negative. My boobs have felt sore... And mainly my nipples for almost a week straight. Anyone ever experience this?!.. I have been ttc for the past year and haven't had any luck. Prior to that had a miscarriage. Ever since I had the miscarriage my periods have been consistent. Anyone have Suggestions? Or Advice?