You can become pregnant anytime you have unprotected sex. Irregularity doesn't necessarily mean infertility.
yes. as a matter of fact, i recently got pregnant. my periods were so irregular for the past year that they were mostly 10 to 20 days late. sometimes even more days. i never got pregnant when my periods were normal (every 28 days, right on time) but got pregnant when i least expected. so yes you can get pregnant any time as long as you are not menopausal