I have a baker's cyst in my left leg and my knee is hurting why is that? and how do i get rid of the bakers cyst?

Steroid injection.: Baker's cysts can be painful. However, knee pain is so common that you may well have another cause. Hard to say without more history and symptoms. Initial treatment of baker's is a trial of steroid injection into the knee.

Meniscus: Bakers cyst are usually caused by fluid from the knee "leaking" out the back of the knee through a weak spot in the lining of the joint. This weak spot is usually caused by a tear in the meniscus. I would recommend a visit to an orthopedist and possibly an MRI to evaluate that meniscus as with your young age a repair of any tears would be best treatment.