I have 4 swollen lymph nodes in the neck for 2weeks had unprotected sex 2 weeks prior ,sneezing and mild headache what can cause this symptoms?

Got a textbook? The possible causes are myriad. Let's just look at one component, your swollen glands. Signify infection upstream of the nodes, which can be bacterial, viral, fungal, parasitic, etc. Perhaps you have an oral infection such as tooth decay or gum disease. Perhaps your unprotected sex is involved, perhaps, perhaps, perhaps... Please check in w your GP.

Lymph nodes enlarge in response to an infection in the area. You may feel the nodes every couple of weeks, if any of the lymph glands doubles in size, becomes painful, ulcerates, or other nodes become enlarged, or you develop fever, or lose weight, you should see a doctor. Wish you good health!