Could I be pregnant while on birth control?????

Patient: I have been on birth control now for about 1yr and I just had my period about 2-3weeks ago and all of a sudden yesterday started bleeding but it is a dark brown to a brownish red. I’m only in the middle of my second week of the new pack of bcp. I did miss a couple of pills last week that I never took and 1 this week which I took 2 the next day. Have been having lots of lower back pain the last 3 weeks and was a little nausea this morning and cramping for last couple of days. So wasn’t sure if missing the pills would cause this or if I may possibly be pregnant??? Never had this before but have people in my family who have gotten pregnant on birth control.