Periods changing after miscarriage

I am 19. My periods use to be 30-34 days apart. However, over the last year since my miscarriage, they have started to get shorter between periods. 10-15 days. My most recent one was only 9. my periods days have gotten longer they use to be 5-7 now I bleed for 7-12. I know I am young but has anyone else had this problem?