Cant help but feel like a failure

Welp momma's I'm finding today was a tough one. I am breastfeeding my 3 week old baby and it is just so much harder than I imagined. Since day one he has had trouble latching, I've been using a nipple shield off and on which helps and solves the issue basically, but I want to feed him without it so bad so I try all day without it. He pulls off the breast and will cry, it's hard to get latched and when he does it isn't for long. He wants to eat every second that he is awake, he always shows hunger cues but sometimes won't eat which confuses me and makes me think he isn't getting enough milk but the Dr says he has gained more than expected. He has posterior tongue tie, idk if I should get it fixed or not, between that and my flat nipples I feel like a failure. I can't afford to formula feed him nor do I really want to. I want to feed my baby when he is hungry and I suck at it. I can't stop crying I want to be a good mom so bad, I love him so much I don't want his to ever feel discomfort. Just needed to vent, any words of encouragement appreciated.