What is shown on a medical report sent from dr to employer?

my work is being particuarly nasty because ive got an undiagnosed illness for which i need appointments for tests. i dont htink my manager thinks i am genuinley having appointments (evne though i am) and he went to HR and complained. HR want a medical report from my Dr. I dont have a problem with this but want to know whats on the report? every illness ive ever had? everytime ive been to dr? who dr has referred me to? the fact i had an STD? i mean how much? the fact i was depressed? or is it just the last couple of years? how detailed? im embaressed about some of it. but i want to prove my innocence. can it go against me if work find out i was depressed and see a psychologist? At least theyll see the truth about my current illness.