Time off from work because of mental health issues

Hi everyone. Ive been struggling with my mental health and I need time off from work. How long I can be off from work for mental health issues? My contract says 120 days on short term disability so I guess technically I could be off for 120 days. But I don’t know if I need that much or the doctor would agree for that much? I don’t know what to expect. I also feel like 120 days is not enough for what I’m dealing with. I don’t have any friends I can ask to so I need some advice here. Usually is it possible to be off from work for mental health reasons for a few months or am I wrong?