Anyone else have very short AF?

I'm 22 and for the past year my AF HAS been lasting 2 days. It'll start with light brown spotting and then I'll have 2 normal period days and then ends with light brown spotting again. They come every 27/28 days so the timing is right but the length freaks me out. I told my doctors and they say it's fine and normal. I do not know anyone my age that has periods this short. I have gotten my regular physicals and pap spears but I am afraid there is a disease that has not been caught or I may just be menopausal. I'm not ready for that because I still haven't had kids and I want to try having kids as soon as possible once my fiancé and I have a home together. I don't know if short AF has anything to do with fertility issues.