Regular to irregular?

I first got my period when I was 9 yrs. old (I know, super early). From when I first started (4th grade) till I was 16, my period was super regular and I knew when I was about to get my period. Once I started becoming sexually active, my period would start coming a couple days before or after I predicted. No big deal. Now that I’m in college, my cycles have been so irregular! Sometimes I miss two months in a row and it’s very stressful. Is it normal for cycles to change that drastically? Did anyone else have this change? Is there anything that helps regulate it again besides birth control?