Hi and welcome,
More than likely, what you have is not technically a hemangioma. That is the term for a birthmark that goes away by the time puberty is reached (usually earlier). However, back then, doctors called all vascular type birthmarks "hemangioma."
I think you might have an AVM or arteriovenous malformation or some other sort of vascular malformation. I'm telling you this so that when you do your research, you'll look under different terms and maybe find more information.
Because these are vascular, it could very well be causing pain, especially if you are under more stress.
Do you have a physician you can see about this?