What Could Cause Delay In Periods?

I've been taking Ortho Tri-Cyclen for about 2 months I just started my green pills three days ago and no period and i have very strong signs of pregnancy now. also for about a week i've just been very blah and completely exhausted. I've never missed a day of taking my pills but i don't always take them at the same time. I've already taken a pregnancy test and it was negative. what are the chances that i could be pregnant since i don't take them at the same time?