Severe migraine for about two weeks. No seizures or any other symptoms other than feeling weak and tired. Should I be worried about a brain tumor?

Migraine. Whenever there is a change in the nature of your migraine, you should see your own physician who treats it.
No do not think so. Is this your first migraine? It's not common that a headache is the symptom of a brain tumor. A migraine may last two weeks, sometimes longer. If anything, brain tumors cause mild headaches. Have you been working on anything to help stop this long lasting headache? Extra sleep? Dietary changes? Headache medications, like preventers?