HELP GIRL IS STRESSING!!!

I’ve started a new pill almost a month ago now and it’s a non break one. Where I have no period. I’m on my 2nd batch of pills and I’ve had this heavy brown bleed for 2 weeks now and I have no idea why? I’ve read it’s due to change of my pill but I’m worried I’m pregnant!! Me and my partner had sex on the 24th December last and he did cum in me but I was taking the pill on time etc? Worried. Please help ASAP!!