Some good responses on here. I agree that this is not an issue with PhDs in general.
In my opinion it is a wider issue. Undergraduates are plagued by this mental fragility and it appears women suffer more than men.
I think that young people are definitely more prone to this than other generations. Facebook and all social media in general has a huge deal to answer for because it breeds isolation. Lazy parents who cover their kids in cotton wool and protect them from everything are a scourge on this generation as well. Add to that the pressure heaped on kids by teachers to get good grades and go to university as the only way to succeed in life with no regard to whether the person wants to go and you have a recipe for disaster.
Then you add in the infantilisation of undergraduate students by academic staff who treat students with kid gloves in order to secure favourable student reviews and a culture of political correctness and the perma offended who discourage any sort of disagreement of views because they have deemed it disrespectful to hold a different opinion. We have a whole raft of people out there telling us what to think which inevitably breeds resentment. Then you have this laughable framing of every single referendum amd election as a fight between good and evil which means those on the losing side no longer accept the wishes of the democratic majority and you have to wonder why anyone nees to ask the question of where depression comes from. People dont properly respect each other any more. People dont respect the right of others to hold different views. People have become more self obsessed. They believe that they are vitally important because nobody in their life has displayed any honesty towards them for them to believe any different. So for twenty year they are told they are a star but the reality is that the overwhelming majority are doing a bang average job, earning a bang average salary for a bang average company IF THEY ARE LUCKY.
People are way too obsessed with how others think of them and it clouds everything they do.

The question should not be why id mental illness so rife.
It should be why so many people manage to survive this WITHOUT breaking.

The obvious problem is that when you do a PhD or take a job, real life kicks in and it is brutal . Many young people find themselves ill equipped to cope without safe spaces, nurturing environments or a host of other people prepared to wipe up behind them.

My advice is to gather people around you with a variety of views and opinions who will be honest with you. Secondly, get over yourself. Thirdly, try and do things which bring meaning to your own life. Finally, screw anyone else who would criticise you for living your own life.

I would echo the comments of PracticalMouse.
You really need to focus on what you can control.
Forget the politics and focus on the fact that your thesis is not up to scratch.
Fix that, get your PhD and then I have one final piece pf advice.
Find a new job. You have been there too long to the extent that the office politics is affecting you.