It can be an alarming bit of advance, but consider this: You don't need to be happy all/most of the time. Happiness is especially ellusive if you focus on attaining it directly.
Read about ACT Therapy if you can - where I first learned this advice - it gets you to internalise this strategy to have a better relationship with feelings:
Accept your inner experience (and be in the moment)
Choose a course of actions based on things you decided you value
Take action
We can't change the way we feel, at least not reliably, which means that its best to "accept" feelings (there's a specific meaning of "accept", and doens't mean you have to "like" your feeling), and we can almost always direct our attention. In almost any situation you have the power to _temporarily_ focus on something, and you can just keep diverting your attention, it's like a super power.
Separate to ACT, I've found mantra's such as the following helpful for dealing with strong episodes of emotion:
Let it come.
Let it be.
Let it go. [Exhale slowly]
A much simpler one for a strong episodes of anxiety/sadness/dysphoria:
"There's nothing I need to do about this" [At which point I usually choose something to do or think which is important to me].
In saying all of the above, some of your issues may be situational (or not, could just be an internalized playbook of beliefs), which is where getting professional help comes in, to help you work that out.
Some practical steps you might take once you have a strategy for managing your mental health: Look for an alternative living arrangement, a different (or same) job or pursuit (if not for supporting yourself financially, it will open up opportunities for social interaction and engagement). Figure out what things you value, or have valued in the past if you are too depressed to connect with that; then let these form a compass point for you.
Becoming a monk will probably mean you have to face yourself head on and you won't have conventional support - do not isolate yourself. Whatever you do, choose something that has a good chance of being absorbing and deisolating.