ULPT request: What problem/illness could put me on sick leave for like 3 months

Tldr at the end

Basically i'm being bullied at work by my colleagues. It escalated quickly last month. My psychiatrist accepted to put me on sick leave for only 3 weeks on the condition that i see with the union rep either a way to get out of my job and still get compensation (like unemployment benefits) which is near impossible because my employer is known to NOT accept mutually agreed termination and to NOT fire people and usually letting them in a limbo until they purposefully abandon their post or commit a gross misconduct OR tame the bullying situation. The problem is that since I don't have any proof, and the only witness I could have will not come forward because she wants to stay here long term, the only thing that was suggested is a monitored talk with the 2 girls that treat me like shit. Needless to say that it was a categorical no for me.

The only solution I have is to be on sick leave until the end of my contract (in june) so i'll still have benefits and won't be stuck in a room with 2 people that hate me for 5 months. I doubt my psychiatrist will accept to put me on sick leave for that much since she was already a bit reluctant to get me off work for 3 weeks.

Does anyone has any idea for an injury that could get myself multiple months of sick leave and won't have a big impact on my future? Can't be anything mental bc I'm on meds that make me stable and my psychiatrist knows it.

TLDR: need to be on a long sick leave bc coworkers bully me and my union's only solution is to just talk and i won't get any benefits if i resign. Need a good illness or injury idea that would put me out of work for like 4-5 months (i put 3 months in the title but it was a mistake)