late period

Nikkie
I was on birth control about a year ago for a couple years. I got off it and months later my period started acting up. 
I'm late every month or sometimes I skip my period. 
I'm constantly worried every month about being pregnant but I don't want back on the pills and shots because they made me suicidal.  
I'm also 21. 
I generally have a period for like 3 days. 
Lately they have been the same time but with extreme cramps. 
Should I see a doctor?
A couple months ago when I went in about this she told me to not be worried but I feel like this isn't normal.