DD is 71/2 mos and she has been beating me up since day 1!!! I've found that these things help keep me sane:
Keep her nails short- trim them or bite them every day!! ( This is also important b/c she plays with her privates all the time now and I don't want her hurting herself or introducing bacteria. )
Redirect her when she is grabby or pinchy to a necklace or hand holding or a silly game
I make regular tasks into a game. Once I realized she knows Topa ( a game my Dp's Spanish family plays where they bump heads) and would lower her head and tap yours with it, I knew she was capable of learning some oher games so we have a nursing bouncing game and even a nursing swimming game. It's fun.
If it hurts I won't continue to let her do it. The last thing I want is to get angry, resentful or even irritated.
I also teach her how to "pet" babies and cats and dogs all a little bit differently, but always saying "Gentle...gentle...gentle..." the whole time. She has begun to "pet" babies very gently and also kitties. I taught her to pet the dogs a bit more roughly, but she is still surprisingly gentle with them too, much moreso than other babies I see. Maybe you can teach ds "Gentle" with mama. Show him how to be affectionate.
These things really helped. I know a lot of WAHMs here at MDC make nursing necklaces. Many are made to look just like regular jewelry. You don't just have to use them when you're nursing. Also DD thinks it's funny when I exclaim in pain. She gets a kick out of causing it, like if she pinches my nipple with her fingernails and I yelp, it's like a button she can push to make me yelp. It's a normal part of development, but I'm trying to take some of the fun out of it for her. Also, she doesn't know when her nails are long or short, so I trry to be consistent. If she does something one day and it doesn't hurt, I distract her on a day where her nails are too long and they make the same thing hurt.
Finally, kids are typically over 3 and always older than 2 before they truly realize they are causing pain. They can learn not to do a certain thing, but they don't REALLY understand why. I can't remember the true age at which they realize that pain hurts you and the dog and the cat the same way it hurts them, but it's over 5. Maybe 7? I can't be sure. They can grasp the basic concept, but not the abstract idea of empathy. So, your ds won't really understand for a long time. Stay strong, mama. It will get better.