I started my period on the 12th of march & ended on the 17th i waited a day or two to have sexual intercourse i've started spotting and still is spotting and i don't know why & i'm very concerned.

Irregular spotting: Spotting between periods is a common problem that your Ob/Gyn physician should evaluate. It could be just an irregular cycle due to temporary hormone fluctuations that maybe will resolve without treatment, but it could also be due to something abnormal that needs treatment. Depending upon your age and other medical conditions, your doctor can help determine the cause.