>No, I think that's pretty normal. I do it all the time.
[Edit: Currently I "listen" to a lot of Georgios Papadopoulos, heh!]
>I can even "compose" my own music
I can relate! Unfortunately, I'm totally untrained regarding music. I once tried to enter one of the melodies in my head (simplified) into a music program, and it took forever, because I had to find the correct notes by trial and error: "Not that one. Neither that one. Still wrong. Not quite. This one is it! Next note..."
I think this kind of trial and error is actually the best way of learning an instrument. My guitar teacher did exactly what you did (but on a keyboard) when he was a kid, and even got feedback from his parents on whether he hit the right keys. He's a hell of a guitar player now, surely among the (subjectively) very best in my country.
> it's so slow and frustrating that the melody in my head just disappears.
Use a microphone to record yourself humming the melody first, so you can get the original back if you forget it.
Separately, I'll mention that imitone (https://imitone.com) works surprisingly well. The transcriptions don't come out perfectly by any means, but they provide a base that you can then clean up.
[Edit: Currently I "listen" to a lot of Georgios Papadopoulos, heh!]
>I can even "compose" my own music
I can relate! Unfortunately, I'm totally untrained regarding music. I once tried to enter one of the melodies in my head (simplified) into a music program, and it took forever, because I had to find the correct notes by trial and error: "Not that one. Neither that one. Still wrong. Not quite. This one is it! Next note..."