Am I likely to be pregnant?

[terrifiedmaybeneurotic]

Ok so. A couple of weeks before I went to see my boyfriend, I started taking birth control (the progesterone only pill with no placebo pills). We had sex the first day I was there and he came inside me. Then I was really paranoid that I hadn't been taking the pill right, so we rushed to the pharmacy and bought a plan B one step. (later realized I hadn't been taking the pill wrong as all my pills are the same and have to be taken every day - I just got scared for some reason). I took it probably less than about 9 or 10 hours later. 4 and a half days later experienced light bleeding (was browny red). It's now two weeks and two days later, I'm experiencing some menstruation-like cramps (have been for maybe two days). Is this my period coming or am I likely to be experiencing early pregnancy cramps? I know I probably sound crazed but I'm terrified right now. Many thanks