What Causes Light Menstrual Bleeding When On Birth Control Pills?

Hello. I use to take birth control pills in the past and never really had much problem with them. Well, one month ago I started taking the pills again and I am on my first pack. I missed maybe two or three pills but always followed up with taking two. I think I only missed one pill and flushed it. I started my period (I think, I fisnished my last sugar pill last night) and my period was very light not like my normal heavy flow, brown even. I recently was hanging out with my boyfriend and he fingered me and we had oral sex. Is there a chance I could be pregnant if he got cum on his hand then inside me? Am I protected? Is that why my periods are messed up?