What I learned in jobs is don't stick your head above the parapet, personally I go to work, do my job and come home, I'm lucky in that my current job I would fly to the moon for the colleagues I work with, if it would help them out, the three people I work with the most are lovely

I'm sorry you don't currently get on with the people you work with, do they know you have mental health conditions (as in, did you declare them in your application) ? There's arguments for and against letting people at work know about difficulties you have, legally although fat shaming isn't illegal, if you were to let them know about your limitations due to mental health, legally they couldn't discriminate against you, even by making comments about the length of time its taking you to learn stuff - for example I have learning disabilities so I would find it hard to learn stuff quickly in a new job, I'm not sure what your mental health disagnosises etc are, I hope they are taking them into consideration if they know about them