I was diagnosed with endocarditis the doctor asked me if i'm an iv drug user. i told him no... what are other causes of that?

Many, many things: You should have an echocardiogram, if you have not had one already. Most people who get endocarditis (an infection - usually bacterial but may be fungal and others) have a previously damaged valve, sometimes from rheumatic fever or mitral valve prolapse and then get germs into the bloodstream, sometimes from a dental procedure or even brushing teeth, particularly if there is bad gum disease.

Several other causes: The doctor was correct to ask! IV drug abuse is a common cause of endocarditis. He needed to know if that was the reason, because then both problems can be addressed: the infection and the drug abuse. Other causes may be bacterial, fungal, etc. Sources can be the mouth, urinary tract or colon, from recent procedures. See: https://en.wikipedia.org/wiki/Infective_endocarditis#Infection_setting