I have had swollen lyphnodes starting from my neck armpit to chest plate and breast for 5 months now what could it be?

See your doctor: Your lymph node enlargement suggest a number of things including virus infection such as "mono", or other virus, a skin condition to which lyph glands may be reacting to, other types of infection such as a cat scratch disease or even tb, or malignant disease of lymph glands. An autoimmune disease such as lupus may do that, or a drug reaction. The best thing would be to see your doctor.