If you are having trouble breathing, then please see a doctor soon before it becomes an emergency. You could have some sort of bacterial infection or virus, like mononucleosis (EBV), strep throat, sinus infection or some other upper respiratory infection. Your thyroid could be enlarged due to goiter either from hyper- or hypo-thyroidism. Your parathyroid gland could be enlarged. You could be having an allergic reaction to food, medication or something else in your environment. Goodluck!
Relax no need to worry it is indeed common to notice enlargement of one of the glands (lymph nodes). It is an indicator of the ongoing infection, probably you will be having pharyngitis or laryngo pharyngeal reflux which is causing you the above problems. Try avoiding coffee/tea/fizzy drinks for few days and drink plenty of warm water. If the symptoms persist please do consult your doctor.