Just wanted to send some support. I could have written the exact same post about 4 weeks ago. I started sleep training (sh/pt) with my now 14 week old as he was addicted to sleeping with the boob. He cried a lot at first but now he now can go to sleep on his own in his crib and STTN twice (more often one or two wakings per night but using the sh/pt to get him back to sleep. also still working on extending naps during the day).
My LO never seemed to cry before EASY too. I felt terrible when I first started. Just know that it gets better and you're doing him a huge favour by teaching him to sleep independently. I had to keep telling myself that it would work and it will. It's just really hard at the beginning. You're not hurting him, he's just frustrated because he's not getting what he's used to. It really is a gift to allow him to sleep on his own, it's just hard work at the beginning.
Also, as a word of advice, I ended up in some more AP by keeping him on my shoulder for too long (he got used to falling asleep there). Try moving to sh/pt in the crib as much as possible or as soon as possible.
Good luck! Stick with it. You're doing the right thing!