if it were me, i'd have a very clearly specified plan in place about when (not that you know exactly) you'll be on leave, and when and how you intend to come back.Â
do you have a human resources department? if so, i would be tempted to discuss it with them first.Â
are you in the US? unless you've transferred or something, you won't get FMLA protection if you just started-- you are only guaranteed FMLA if you've worked somewhere a year. truly awful. your company/place of employment might have something "generous" in place, though. It's doubtful that your boss would know, that is more the realm of HR.Â
so.. if it were me, my plan of action would be: Talk to HR. Find out what would be guaranteed to you, how much time you could take, estimate your leave (approximated, if you can plan it between now & then) then write up a plan, saying i will go out x date, return part time or full time x date, etc etc. then make an appointment when the boss is in a good mood, and show him/her what you've drawn up. it is much more professional and harder to argue with if you've figured out the details.. and from what i've seen, that is often a relief to the supervisor to not have to make those decisions or ask you to.