I think that your son is finding it hard to adjust to not being the baby. If you decide to feed him again it needs to be on your terms, and it needs to not be in a way that "rewards" him for being tired and surly. Will he calm down outside, or in a car, or in the pusher??

Do you have a sling for DD so that you can feed her on the run and not have to interrupt whatever DS is doing??

Good luck!