I wouldn't draw it straight to a brain tumor.
If you want to draw it to brain tumor... you need to research the human brain and find where and what exact section of the brain where a tumor would make ties between headaches and sneezing.
Considering it's finally spring, pushing to summer the weather is must nicer. grasses grow and pollen flies. flies fly.
It could very well be that you are overcoming something that is rather common that might be irritating or causing pressure in your sinuses. Sneeze headaches are the worst. When you sneeze your entire facial muscle clench harder than you did when you pooped yourself over the brain tumor fear.
it's painful, that's pressure being pushed through sinuses as well, There is a lot of things that cause headaches, even the bright of day sometimes.
I am in no way being rude or satirical, I just want to lighten the anxiety of a brain tumor and possibly consider some other causes too. Hell, my girlfriend has been sick with the flu in April, she feels horrible... and is in a lot of pain right now. But it hasn't hit me yet.
transmissions through air and touch are amazingly fast and sneeky, you could have easily caught something.
Give it a couple weeks. If you have these constant symptoms for this duration... or it becomes unbearable seek a professional. If you jump in the game too early, you're going to be paying out of your ass for medical bills my friend. You've got to be honest with yourself, I hope the best.
Keep us updated.