Lots of things can make them irregular - Polycystic Ovarian Syndrome or PCOS, stress, travel, illness, thyroid problems, being overweight or underweight, hormonal imbalances. It is a common misconception in the medical community that the pill (or any other hormonal contraceptive) will regulate things. All it does it produce a phony cycle while you are on it, but once you come off the problem still remains. The pill hides the problem, it does not solve it. Your best bet is to find a knowledgable doctor who is willing to get to the bottom of WHY your cycles are irregular, instead of covering up the problem with the pill. The doctors who do Napro Technology specialize in this, they are an option to consider.
http://www.fertilitycare.org
The only way to know if your cycles are truly annovulatory or not is to chart. My cycles are usually between 45 - 90+ days long. I have ovulated as late as CD61 before, or as early as CD23. And yes, some of them are annovulatory too. Just because your cycles are long doesn't automatically mean you are not ovulating.