Flow and could I be pregnant? Please help

So usually my periods are really heavy and last for 7-8 days which is a normal cycle for me. This time my period came on time but was super light to the point there I’m just going to say it was spotting. The blood from this ‘cycle’ was brown and old. Me and my ex had sex two months ago and I’ve gotten my regular as normal period twice. When we had sex in August I took plan b. I was wondering why my cycle is like this and if I’m pregnant or not. Please help