Getting pregnant with irregular periods?

Okay ladies, so I'm currently trying for baby number 2. My son is now 4 and until September of last year I had the Mirena IUD. But since then we've been trying and nothing. Since I got off, and even before my first pregnancy, my periods have been irregular. The last year, they've been irregular, but in a pattern, if that makes sense. For example these were the dates for the past few months: june 16-23, July 21-28, Aug 17-25, Sept 21-28.

Now this month nothing yet.

My question is, for those of you with irregular periods, how do you know when is a good time to test or if it's too soon?

I've had what I think may be symptoms, such as crazy mood swings, cravings, fatigue and weight gain. I'm not sure if it's my period coming, or possibly pregnancy. But I could be psycing myself out..