I'm 23 years old, I've been irregular all my life. I haven't had a period for a few years been trying to get pregnant, but nothing. Why don't I get periods?

Infertility problem. A 23 year old with no periods for several years and difficulty getting pregnant implies a hormonal or endocrine problem. There could also be anatomical problems with your uterus or ovarian egg production. I visit to an infertility specialist is advised, assuming you have been trying unsuccessfully for more than one year.
No periods. There are many reasons women do not get regular cycles, including thyroid disease, elevated prolactin levels , female hormone imbalance, pcos, and menopause. It is important that you see your obgyn for an evaluation or a fertility specialist if you desire to conceive. Some women who do not get periods are at increased risk for endometrial cancer and other diseases. Go get evaluated!
No periods. Irregular or no periods usually means irregular or no ovulation. If you do not ovulate (release egg) then you will not get pg. The problem with being irregular is also that you do not know when you are fertile. We have medication for this. You need to treat the problem for both fertility and health reasons. Also need to check for sperm and tube problems. See specialist.