Why is my head always singing?
Don’t say always. I don’t think it is always singing. You must have used that part of your brain more, i.e., the right side of your brain, and so music comes to you naturally.
Another alternative is to spend some time solving puzzles. Like crosswords, then you use the other side of the brain. You can sit down and count numbers; do some mathematics, or count money.
Do those activities that will the balance the other side of the brain. Or read something, or listen to knowledge.
Now you are listening to knowledge and your mind is not singing. So, reading, listening, counting, all this will help you to activate the left brain as well.