Do i need to see a doctor?

I got pregnant in December 2013 and before that my periods were so irregular i would go sometimes months without having one... Well now that my son is 4 months old I had 1 real period last months and this month it hasn't came yet I get cramps bad tho every month when my period should be here just no period its been like that since I was 15 ( when I first got my period I'm going to be 18 soon) also can't be pregnant my husband is in the army and I just got to him two days ago