had period for 3 weeks

Hello! Have you started or stopped birth control pills recently? They have a habit of interfering with periods and menstrual cycles.

Do you have any other medical problems that you know of? Do you have any accompanying symptoms?
For example, do you experience pain during intercourse, have you had other strange bleedings like too heavy, or spotting or anything similar that could relate?

It is hard to say just like this with no additional symptoms. Are you on some kind of medications? Different kinds can affect periods.

If you have problems with your thyroid gland, you are more likely to have problems with your periods as well.

Ovarian cysts often cause no other symptoms but could interfere with periods, hormonal imbalance and all sorts of different things.

You age is an important factor as well as information if you gave birth, have sex, etc

I am 22, have an overactive thyroid gland, and my periods have always been on time, regular since the birth of my child. But my last one lasted for 4 weeks! What does that mean?