What is a headache, stomach ache, and stuffy nose symptoms of?

Many possiblities: Symptoms as nonspecific as these could be from a viral illness that has to run its course, a bacterial illness that would respond to antibiotics, an allergy that would respond to allergy medicines or to removing what irritates you, to any combination of the above, or to something else entirely. The way to find out is to go to your doctor for an evaluation.