Strange rash on upper arm, what could it be?

Hello everyone, I have the following red, crusted spot with white pustules on my arm. It doesn't itch, but it's a bit painful when pressed, like a bruise. Appointments to a dermatologist here aren't available for months unless it's an emergency. What do you think? Is this necessary to get checked out quickly, or is it harmless and can wait?

It does worry me a little, I haven't found any similar spikes online.

I know there's no medical advice here, but maybe someone has experienced something similar? Thanks in advance.