There is always a chance of getting pregnant during unsafe sex, even if your periods are irregular.
Also, if your periods are unpredictable, it is more difficult to know when the 'safe' times to have sex are - or be able to tell when you are late. Therefore, it is important to use contraception all the time if you don't want to have a baby.
Of course, if you are trying to get pregnant, then you could use an ovulation testing kit to learn about the best time for you to conceive. This test will give you a rough idea of how likely you are to get pregnant during a specific point in your cycle.
If instead you are worried that you might be pregnant and wasn't planning to conceive, now is the best opportunity to take a test to find out for sure.
Even a cheap test from the chemist will show a result. If it comes up positive, then that's more than likely the correct result. However, if it is negative, and you still don't get your period, I would advise doing another test in a week or two.