What Causes Early Menstruation Along With Dizziness?

Hi, I m 39 years old and had my last period on February 8th. My boyfriend and I had sex on Feb. 10th al the way to feb 16th. Last Saturday February 21st I start having periods and its heavy feeling dizzy time to time.. I have regular cycles 28. I don t know what could possibly causing of these two periods in one month. Could i be pregnant or anything feels help.. I m worried Thanks Ysabel