I don't know how qualified I really am to give advice on this. I was awful at taking criticism when I was younger (teen and a smidge after). I'd go as far as to destroy my creations for getting one off comment. It's something I just kind of grew out of.
Granted, my "growing out of it" had a lot to do with finally escaping a shitty environment and not being bombarded with a parent calling me useless and whatever all the time lol-- which is exactly why I'm not sure if any of my advice means Jack. But eh, I'll say something regardless.
It is a skill that has to be grown along side a lot of other things. Self contiousness and inability to accept flaws in other aspects of your being can totally feed into not being able to take feedback on your creative outlets and that is a HUGE thing to try and conquer. No one and nothing is perfect; that honestly expands to everything. No. Nothing you write will be without flaw, that's something you have to accept. It'll never be "done"; you'll always be able to tweak wording or use a different word or whatever. Keep it in your head as always a work in progress. Until that shit is printed and bound and off the printing presses you can change it, better it, feedback isn't saying your finished work is bad because it isn't finished. Feedback is helping you improve this work in progress. And the best part about feedback: you don't need to take it. Sooo much of that shit is super up to personal taste. You know how many times I've gotten contractions in feedback? "Why is your style so needlessly wordy?" "I love how vivid the descriptions are." / "You use so many archaic and big words, It really slows down the reading..." "You're vocabulary is so robust and impressive!" / "This seems unrealistic..." "These characters seem like real people, you can really understand them!" Heard it all, man. Unless it's editing feedback you can really pick and choose since that stuff can be super subjective. Suggestions you can either take or drop. (That said, I'd still suggest taking it and not dismissing it all outright lol. Hold onto it and think about it with a clearer mind and reallt ask if it'd be better changed or not. Don't do this while emotional.)
Taking things to heart isn't helpful. The sooner you learn to laugh off mistakes and say 'damn you right, I'll go back and fix it or tidy it up or whatever' the better you'll be. That is, unfortunately, a skill that has to be honed. Until then, it's a real "fake it til you make it" type deal. I was darn right embarrassed by my own reactions so instead of having a meltdown or just feeling (and probably looking) sorry for myself I consciencely make myself react in my fun little care free persona way. Laugh at my own mistakes, say "okay thanks," even if I think their suggestion is stupid, keep their ideas written down to reflect on later. (Seriously, don't dwell on these things with raw emotions. They'll help you more if you can really take them in on your own time.) I forced myself to sign up to an IRL writing group to force my ass to sit there in awkward stewing for an hour and a half to deal with these bad feelings and sit with them. See it doesn't really matter, see how gracefully others take feedback, emulate that grace. (Sometimes someone will give you the dumbest feedback and you get to watch everyone else defend your work and BOY THATS AN EGO BOOST). Plus giving others feedback really makes you think about how people think and feel when giving you feedback. It's so mundane. It isn't out of malice. It is to try and help and share thoughts. Exposure therapy, if you will, but only if you think you can handle it. I've been going for 7 or 8 months and I still shake like a leaf each time it gets to my turn so it is a very hard thing to do (that or it just hasn't helped my fear of public speaking/reading my work outloud), so maybe just hold onto that idea until you've honed the skill yourself a bit.
As for how to feel confident again... well, I'm gonna be real, I'm still not confident in my work. As long as you trudge on, try your best, keep improving, what does it matter? I submitted a section of my book to my province's professional editors recently and the whole time I felt like shit about it. I'm waiting on a 2 page essay and 30-60minute meeting to discuss my work and I'm shitting myself over it. At this point they probably can't say anything worse than what I've said to myself-- but you know what? At least I did it. And at the end of the day that's all that matters. Point is, let that feeling of not being good enough drive you to be better and do not let it hold you back. Writing and posting it or submitting it to places will have the same outcome weither you're confident in it or not. Maybe you'll never be confident, maybe you will. Cherishing accomplishment is far more useful in my opinion.
This was very much a ramble and I'm not entirely sure how much sense it makes, but eh. That's what ya get for asking internet strangers.