I Took Plan B An Hour After Intercourse After Condom

I took plan b an hour after intercourse after condom failure on the 27th of December. The 1st of January I began spotting and bleeding . It ended about 4th. Which I just ended my last period the 22nd of December and I don't know if that will cause my regular period to be late... I'm supposed to have my normal period the 18th ... I'm experience headaches and a lot of gas and some lower pain in my back. I'm just very nervous due to the fact this is my first time ...what are the chances I'm pregnant???