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I understand your health issue. You need not worry about it at this stage. The green snot is nothing but a collection of infected mucous. when cold viruses infect the respiratory tract, the body makes clear mucus that helps wash away germs from the nose and sinuses. After about three days, the body's immune cells fight back, changing the discharge to a white or yellow color. As the bacteria that live in the nose grow back, they may also be found in the mucus, which changes to a greenish color.
To get rid of this symptom, it is necessary to evaluate the cause of such infection. The most common cause being sinusitis. I would advise you to consult an ENT specialist where he might ask for a simple PNS (Paranasal sinus) X-ray to confirm the diagnosis. Following which treatment will be started mostly with antibiotics, decongestants and nasal sprays.
Hope this helps. Please feel free to ask if you need further help.