Have persistant, fluctuating headache and general malaise for two weeks, now slightly sore back of neck-no neruo symptoms, etc. could be brain tumor?

Not likely: This is the time of year for viral illness, and you may have just come down with a virus that your body is fighting. However, as your symptoms have been lasting a while, it is a good idea to visit with your doctor for a more detailed account of your symptoms plus a physical exam and possible lab tests to get at the primary cause of your feeling unwell.

Not very high: Without more findings or info, concern of a brain tumor, either benign or malignant is fairly low. While brain tumors may present many different ways depending on where in the brain they develop, headaches are still most common finding. Still, they r rarer than most other causes of headaches. If it persists, worsens, or other symptoms develop, follow up with your md as they mentioned.