when it comes to the body, especially the female body, there's no such thing as normal. Your cycle can be irregular for many reasons, including stess, diet and whether you're on the contraceptive pill, not just pregnancy. I think the average length of a cycle (that is, the length between your periods) is about 28 days, but can be anything from 20-35 days depending on various factors. If you're worried, pop in to see your GP.