Trying to conceive.

I have an irregular period, and me and my husband are trying to conceive we've been trying for over 4 months now its just really hard to know when I'm ovulating or not and my period comes late every month. The longest I've gone without a period is 2 months. I have twin daughters that are almost 2 years old now and getting pregnant the first time wasn't hard at all I wasn't even really sure how to keep track of ovulation and all that but this time I know more than I did last time and it seems so much hard any advice?