I've developed a stiff neck on the right side along with a swollen lymph node and other symptoms, could this be an infectious disease?

Possible: It is possible that an infectious disease present itself this way ( scrofula= TB infection of lymph node of neck, hiv, ect...) may present this way , other non infectious diseases may present this way also, you should see your doctor for further evaluation.

It could be in terms: Of an upper respiratory tract infection. See. Your doctor if symptoms persist for more than a day or two or worsen . What are the other symptoms-this could help.