I'm at a uni with a college system so I provide this information to both my college and department, am i able to keep it discreet from my supervisor's for the time-being? until I feel /when/if I feel I need to make them aware?

Thanks

Why do you need to provide doctor's note to your college and department? Your medical situation is your privacy unless you needed something from your uni. If you do need something from uni and they need your supervisor to keep an eye on you to keep you safe because of your medical situation, then yes, they will be notified.