Before I go full freakout?

I've had a headache for 3 days now. Today, I found a lump on the back of my head, even with my ear, like, where the ear, neck and top part of the skull meet. (if that makes sense?) It sorta feels like when you have a pimple under your skin, but it feels like the size of a mosquito bite. When I touch it, it affects my headache.

Has anyone ever gotten a pimple under the scalp before? is this possible? Should I be freaking out about a tumor?
Before I go full freakout?
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