Hi @Catarinha - it's really, really hard right now but I promise it does get better. My DD had her tongue tie snipped at around five weeks old and she's eight weeks now. I felt an immediate improvement BUT it was completely dependent on getting DD to latch properly, which was hit and miss - even now she gets lazy and slips back into old 'bad habits' and I might have to take her off and put her back on several times. Sometimes I get lazy too (usually at 3am!) and just leave it if it's bearable, which is bad, I know . . . this means that it's still slightly painful but completely bearable; nothing like the old agony.
I think the key for you will be to persevere with getting the latch right - I found this video really helpful::
As your DS' mouth gets bigger, it will get easier too, as he'll naturally take in more of the areola.
Have you considered pumping and giving your nipples a break by giving a bottle with expressed milk every now and again? I do this - DH does the 10pm and 1am feeds. The rest come from me. I used nipple shields for a few days as well - carry on, if you need them. If I hadn't used them to let my nipples heal, I probably would have given up as I'd started to panic when DD needed feeding; I'd almost recoil, which was horrible.
I'm not quite at the point where breastfeeding is completely painless and enjoyable but I can definitely foresee that this will be the case eventually.
Having said all that, if you decide to switch to formula feeding, please don't beat yourself up! You tried your best! Don't spend these precious few weeks being miserable - you'll enjoy your baby a lot more when you're not stressed and jn pain!