Uncertain: preggo or not?

Ok. So, this is how it goes:

1. Had my period from Dec. 17 until 22.

2. Had unprotected sex on Jan. 4 and we used withdrawal as the method.

3. Then had unprotected sex again on Jan. 8, 9 & 10.

4. But on that Sunday, 10th my boyfriend came inside me.

5. So, I drank the Plan B pill but two days after that (it says you have 3 days, I know "the sooner the better", but I didn't had the money until that day). The day after taking the pill I felt a little abdominal pain as if I was about to have my period, but nothing happened.

6. Now, I was supposed to have my period yesterday (Jan. 18). I'm regular. Just one day late. No big deal. But still wondering if the pill worked. Lately, I've been having my regular PMS but not sure cause they could get confused with preggo symptoms.

Any little help or thought of what could be happening? All recommendations are very well accepted. I just need a little light. Thanks!