Pregnancy Worry.

I'm worried that I'm pregnant because I've had sex without protection but with withdrawal. Precum can get a girl pregnant so I'm still scared. Also, I began taking the pill recently. The nurse told me that my next period wouldn't be a true bleed and that I could still be pregnant. However, last time I was on the pill I didn't get periods. This time, I did. Does this show the signs of me NOT being pregnant?