is a 15 day cycle normal? should I see a doctor?

so I've been getting my periods about every 15 days consistently for probably a year now and I have no idea why. I wasn't even concerned until a friend told me that anything under 21 is abnormal and I may be infertile. I absolutely hate having my period like one third of the time and I do struggle with some anemia but other than that should I see a doctor? is there some sort of hormonal imbalance maybe?

so I've been getting my periods about every 15 days consistently for probably a year now and I have no idea why. I wasn't even concerned until a friend told me that anything under 21 is abnormal and I may be infertile. I absolutely hate having my period like one third of the time and I do struggle with some anemia but other than that should I see a doctor? is there some sort of hormonal imbalance maybe? https://ift.tt/eA8V8J https://ift.tt/2ZNszJJ