Concerned 😓

I've been having unprotected sex for at least 4 years, and have had 4 different partners within those years. 
I'm only 20, and have Cystic fibrosis. 
Recently my fiancé and I have decided to try and have a baby! For the past two years, I got no period at all... But recently I've been getting pretty regular periods for about 3 months now. 
My main question is, is it possible that I might not be able to have children? Since I've had unprotected sex for so long without conceiving and wasn't getting my period at all for a while?
I'm also a tad underweight. Being 5ft 5in and 100 pounds.Â