Talk to Gynecologist on More Than 15 Days Menstruation

I am not married .Muje November me periods nae howy thy i thought k shifting k doran weight uthany sy nae howy but December k end me ho gaye 7 days but in January 13 ko phr sy ho gaye clots or heavy flow k sath at 29 hai it means more than 15 days or flow bi same hai or clots bi even i feel back pain and weakness. I don't know what to do as it is happening with me for the first time. Flow is continues that i have to change pad after 1 or 2 hours