Help I don't know what to do

My period has become massively irregular and I don't know why or what to do. I am under a lot of emotional and mental stress. The chance of me being pregnant is basicly nonexistent. My period went from being 5 days long with 2 weeks between to being 4 days with 2 weeks then was 11 days long and 4 weeks in between before my next one. The next one lasted 5 days and now I'm supose to start again it's been 4 weeks and I haven't. Please some advice.