OP, when you say “not regular,” do you mean as in – less than 21 days or longer than 35 days, or “This month, it was a 30 day cycle, the next, it was 33 days, the month after that, it was 35”? The definition for “irregular periods” can vary according to who you’re talking to, but the bigger concern with the latter is that you might wind up MISSING your fertile days because you ovulate at different times in your cycle. But, that’s generally not a problem if you get the baby dance on every other day throughout your cycle.
If your cycles tend to be LESS than 21 says, that can be a problem with implantation – it may be a sign that you could be ovulating too soon into your cycle (ovulating before calendar day 9 is no bueno) or that your luteal phase (the period between ovulation and the beginning of your period) is not long enough to sustain a pregnancy.
Longer cycles – i.e., longer than 35 days – could also be an indication of problems like PCOS. Or, as is common with people a few months off of birth control, the end result of that. I started taking B6 during my 4th cycle because I was still irregular at that point, and I was taking a POP (not the combination pill), which tend to have the fewest side effects of all birth control.
First thing’s first: Hop on Ebay and get yourself some cheap ovulation predictor tests. Pee on one daily. If you don’t get a positive for, say, two months, definitely raise that with your doctor – it’s a fairly surefire sign that you’re either not ovulating or that your LH surges are so short that you’re not catching them. In either case, that’s a potential concern. If you don’t get a positive during your first month, it’s possible that you’re just testing after you’ve already ovulated or that you’re having a one-off anovulatory cycle – which can happen to anybody.
That said, an LH surge is also not a guarantee that you’re ovulating. Generally, people should get, at most, 2 days of positive OPKs. If the surge is lasting longer than that, it could be a risk factor for other problems…again, PCOS comes to mind.
However, an LH surge IS a good indication of things. You can do that in conjunction with taking your BBT; though of course, your BBT can actually confirm that you’re ovulating – OPKs can only predict the surge beforehand.