What Causes Irregular Late Periods After Birth Control Withdrawal?

Hi,

I have a question about periods/pregnancy.

I went off birth control 2 months ago and my periods have been slightly irregular since...

I was supposed to get my period on January 9th. I had sex on the 10th, 13th and 14th. On one of those times my partner entered me without a condom. He did not ejaculate and wasn't close to ejaculating. I haven't gotten my period yet and so its 16 days late right now. I took 2 at home pregnancy tests and both were negative...is there still a chance that i'm pregnant or could my body just still be adjusting to not being on birth control?

Thanks.