My LO is also 4 months and having some trouble paying attention to nursing.
I can't talk, sometimes he allows me to listen to other people talking.
If I sneeze, cough, clear my throat...oh my, can't concentrate. He snacks a little here and there...I find I love when he is hungry, concentrates and gets down to business.
He never has slept more than 3 or 4 hours, so the night waking is normal for me. Although now he sometimes wants to sleep on me, in the cradle postion. Won't nurse in the night lying down. Sometimes hard to heft his 17.5 pounds up onto my lap when I am so sleepy.
He had his shots on Friday, and did MUCH better than I expected, and much better than when he had the 2 mo ones. He was pretty normal, maybe a little bit cranky.
He also is not napping well. I feel as if I spend all day trying to put him to sleep. He gets a good nap in the morning (maybe 45 minutes) from there, you just never know. Cat napper. Cranky pants cat napper.
So, seems kindof normal to me. Good luck!