Please don’t be too frightened. There are many many satisfied NFP users!.. There are some that may have issues (I’ve learned), but that doesn’t mean that continued education or a change in methods can’t improve their experiences!
Irregular cycles shouldn’t be a problem for NFP! Actually it’s very natural and normal to have cycles that aren’t the same length every month! “The Pill” mindset has changed this fact… women who don’t have a “perfect” 28 day cycle think there’s something “wrong” with them, or that they’re “irregular”… it’s actually quite the opposite!
Get educated! Ask for help! It’s not something to fear!
Oh… more info on NFP since you mentioned you haven’t taken any classes yet…
ccli.org/ has a complete take home course that you can order. They also have lots of great teachers!
creightonmodel.com/ is the website for the creighton method if you’re looking for an alternative to the sympto-thermal.
Also… check out your diocese website. Often they’ll have NFP information and teachers in your local area!