Having Period while still on pill

I have just recently started taking the pill, when my usual period started I took my first pill for that day. I've now been on the pill for about 2 and a half weeks and in my time of taking the pill I've extended my period. I don't take it at the exact same time each morning but roughly around the same time. I haven't missed a pill so i am just wondering if this is something that happens to some people when the begin taking the pill or if I need to consult a doctor.