Is a missed period normal?

I gave birth in November 2011. About a month my son was born I started my period. I began taking birthcontrol again and since then I have had 2 period per month. I spoke with my doctor and he said that it was normal because my body was just adjusting to the birthcontrol. Anyway, I was on it for 4 months. My husband and I were also using other forms of protection. This last months we decided to only depend on the BC since it had been over 3 months since I started taking it. My period is now 17 and I have taken 3 pregnancy tests that were all negative. Is this normal? Can my body still be adjusting to not being pregnant? Or is there a good chance I am pregnant. I am calling my doctor to schedule a visit.  When I missed my period I stopped taking my BC just incase. I'd appreciate any comments from anyone who has had a similar issue. Thanks!

[Abigail103109]

* About a month AFTER I had my son I started my period.

[JaneRae]

Are you breastfeeding? That can scew a cycle.

[Abigail103109]

No. My milk didn't really come in.