Your son sounds like he is at the ripe age for reflux (some call it colic- but my belief is reflux). My daughter started arching and pulling off while sucking - ouch- and "bending the straw" while nursing.
I had a very fast let down and because the milk is sweet, tends to cause more gas/bubbles in the little one. This would in turn cause the squirming and often very physical movements.
She was diagnosed with silent reflux - silent, because she didn't spit up. The doctor put her on Zantac and that seemed to have tamed the problem, but not eliminate it. She eventually learned to spit out her meds and we then tried Prilosec - I think it was. That seemed to have helped a bit more, but as she grew her dose stayed the same and the doc hoped she would grow out of it by a year, like most. When she didn't outgrow it, I went to a Naturopath and she put her on a probiotic and that seemed to balance out her reflux and allow her to eat more than 2 oz. per feeding (yeah, we were up every couple of hours, every night, feeding, with so little intake). My daughter had learned to eat less and more often to help her through the painful feedings.
When my son was born, he was a spitter with his reflux and was easier to diagnose. He always had painful gas and trouble with my let-down. At 2 weeks he was put on probiotic and would either get it off of my nipple during feedings or I finger-fed it to him. This was a huge success in how his little body reacted during feedings. He was able to take in breast milk without the arching and fighting while being so hungry. It definitely tamed the problem for him. He is now 22 mos and still takes a probiotic daily, as does my daughter.
Good luck to you and your little guy. Ask the doctor about reflux.
D.