I'm 16 years old and on the birth control.

I recently skipped my skipped my period for the first time - which was fine.

Then the week after I got my period and have now had it for three weeks.

I'm not sure what's wrong?.

It could be an issue with the birth control- go to your doctor and have things checked out- 3 weeks having your period isn't exactly normal, and it is a lot of blood to lose.