I've had a headache for 6weeks is it possible it could be a brain tumor?

Possible, not likely: Please see your doctor for a complete history and physical (h&p). The vast majority of headaches are not tumor related. Signs and symptoms of a brain tumor: new or changed headache, worsening headaches, vision changes/blurriness, nausea/vomiting, and sometimes balance problems are the most common symptoms. Imaging of the head with ct and/or MRI may be helpful after a complete h & p.

Yes, possible: There are many causes of headaches, but one that persists for 6 weeks is worrisome. It might be from a brain tumor or from other serious neurological problems. See a doctor and get a thorough evaluation; ask to see a neurologist.