I have been taking ortho tri cyclen for about 4 months and I am on my second week of active pillls, well i?

noticed this time that i have breakthrough bleeding. i have never had bleeding between periods like this the whole time i have been taking this birth control. i am scared. what does this mean? i smoke cigarettes and heard that that could do that but it hasn't happened in the 4 months until now. i always have never missed a pill, the only time i missed was a few days ago where i took the pill at 7pm and i usually take it at 2pm. please help me!!