Don't know if anyone is still looking at this thread as the last reply was a month ago but, given a couple of years ago I was in this EXACT boat (BSc and MSc under belt, volunteer experience and getting absolutely nowhere for more than a year), I figured I'd offer up a few things.
1) You cannot let yourself spiral. We will say things to ourselves that would be prosecutable levels of abuse if we said them to anyone else. If you feel your inner monologue going down like that, do ANYTHING, no matter how silly or childish you might think it is, to take your mind off of it. Keep up with hobbies, play a game, watch a cartoon, play with a teddy, anything. Trust me, it helps. I know it is really tough.
2) Being rejected from a job application, says nothing about you. I applied for hundreds and hundreds of jobs before I got anywhere in my field, I got turned down for volunteer roles. You simply don't know who you're up against, it's the one thing you have absolutely no control over. You might have been next on the list for an interview for all you know but someone else (probably in the same boat as you) got lucky this time. It took me 18 months to get a job.
3) Do not compare yourself to your friends, especially on social media. The stuff people put on social media is in no way a balanced reflection of their actual lives, it is always skewed and usually it depicts them as happier than they actually are and they will have **** of their own to deal with. They may not be able to handle the stuff you're dealing with at all and vice versa. It gains you absolutely nothing, trying to compare, regardless of how successful you are, someone will be doing something you'd be envious of.
4) Applying for jobs you're over qualified for, do not be surprised if you get rejected. It is unbelievably frustrating but if you're legitimately over qualified for a post, most employers will pass you over. Hiring someone is investment and all investments require a big up front cost, if you're clearly over qualified they will see they're not going to get a return on their investment because you'll leave the moment something better comes up. It is not a case of "you're not good enough for this role", it's a case of "we think you'll be gone before the ink is even dry on your contract".
5) I've seen several people comment on customising their CV for jobs. This is excellent the absolute right thing to do, one thing you can consider is looking at multiple job postings and see what requirements or qualifications keep coming up. I'm sure many of you are, but make sure you can evidence these in some way, even if it is just "I'm working towards XYZ".
6) Volunteering and networking... do it. These can get you new skills, plug gaps in CVs and potentially lead you to jobs, and if nothing else can keep you busy. If you're applying try and find a named person to talk to about the role, if you have to e-mail your application to someone, talk to them first. Ask questions about the posting, read up on them first if you can and discuss current or past projects. This shows research skills, enthusiasm and is more likely to make you stick in an employers mind.