Help with going off bc?

I have been on bc pills (yasmin) since August. I took the first 21/2 weeks this December then got busy and forgot. My last pill was the 15th. I bled lightly for two days (22 and 23rd) then didn't get my normal pd on the 31st. I ume this is bc I missed the rest of the pack. I have taken a hpt and it was negative. What I want to know is how long before my periods return to normal,and how common is it to get pregnant your first month off bc pills. Thanks.