Help! freaking out!

Okay so I had unprotected sex first time in like 9 months! and took the plan B pill on that 3rd day (says I could take it within 72 hrs) and it was around when I should have started my period. I had some spotting and then took that pill and I havent technically started my cycle! What does this mean?! Does anyone know if that plan b can throw off my cycle? Did I take it too late? He said he didn't cum in me but I'm sure we all know how that goes! I'm freaking out! Any advice?!