Need advice PLEASE!!

I had my Mirena out on 2/4/16. During the 1 1/2 year I had it in I had normal every month periods. Started AF on 2/6/16. 4 day flow. I feel pregnant but I keep getting neg. my AF was due on 3/5/16 and still no sign. I had a blood test done with neg. results. As of today I would possibly be 4w 4d. I have had what I thought was a couple faint positives. I have camping headach nausea breast tender. As of today my period is four days late. I took a FR digital and it said no. What's going on!?