Irregular periods?

Anita • I`m 22 & have been TTC for 7 mon. now unfortunately I have irregular periods. I`ve been in a great and loving relationship with great partner for 5 years.
I've always had an irregular period because I am a little underweight (97lbs @ 5'5) and it never bothered me until I started TTC. I'm not sure how periods work with that. So I was wondering if anyone knows how this works? Are there any women here who have irregular periods and still conceived?