oh boy do I hear you!
I only wish I'd found this site sooner!
My LO is now in her 9th week and what you describe started at 5 weeks!
Thrashing at the nipple, yanking it and screaming, sometimes she'd beat my boob with her hands in frustration!
I would spend many nights in tears trying to figure it out, the worst thing I did (in hindsight) is keep offering her the breast.
She did exactly as you're describing, it was like she was in pain, I even tasted my own breast milk thinking it was tasting weird for her - turns out I could map her fussiness down to the exact second on the hour, for me stayed like this for 6 hours!!!
I always felt like there was no way she was getting enough, I tried giving her a bottle but she would do the same thing, biggest thing for me was knowing when to walk away for a bit.
I'd give her to my husband or gently place her down on her play mat and go and make a cup of tea, deep breathes and 30 mins later try again - generally to better results, but she was still fussy, I thought I was going to go insane some nights, but she and I got through it and I feel much stronger and more determined because of it and love her even more (if thats even possible!) for how determined and fussy she was!
I have no idea what causes it, I suspected she was wanting more milk so increasing my supply, but I did all of the above, and it all worked, it will pass I promise you!!!!!
Another couple of weeks but you will feel better for it - trust me!