I'm going to call in sick for work for two or three days in a row
Are you calling in for the right reasons? Are you sick?
I need to get rid of the pain in my head
Calling in sick for work is normal, but you need to let your employer know exactly why you can't work.  If you discuss your medical condition with your employer, they might be able to help you get the medication you need to get better.  If you skip work without telling them, you could be fired which would make your mental stress even worse.
I'll send a message to a doctor to tell him to send me the diagnosis and I will transfer that to my work.
That's the proper way to do it. Always protect yourself from work backlash and have evidence to support your actions.