On Pill And Sexually Active. Had Light Bleeding Before Actual Period Due. Pregnancy Chances?

I m on the pill for 3 months now and I am sexually active as of recently. The first two times I had intercourse, my partners condom did not break and I take the pill around the same time every day. My period was suppose to arrive today but it did not come. I did, however, wake up to light bleeding four days ago. It was short-lived and followed by a day of spotting. Could I be pregnant? Could that bleeding simply be a light period? I never had one that light before- I usually have them pretty heavy- but I have been very irregular with my periods in the past when not on the pill.