What Causes Delayed And Irregular Periods?

Hello, I am 22 years old not sexually active ..I have almost always late periods , I went to several doctors and it was the same result: a hermonal problem. But last month s period was dark red and it was a light one .this month I m late again but the problem is that I got the beginning of the period ( brown almost red discharge which I always have in day 1 before it starts) but the day after it was gone ( back to white discharge) ..two days after the same thing happened , and it happened again today but this time it was a drop of blood ..for your information lately I had a viginal infection. I m really worried if this is a serious probleme or it was because of the infection . Waiting for your answer thank you