sigh...i just went through this with Peanut and since it's been a pesonal experience and watching her struggle for days to poop, I swear I will NEVER not give her any foods with not enough grain/fibre in it. If you want my opinion, I think raw is a bit too much for a kittens' stomach to handle. I also firmly believe, now since it happened a few weeks ago, that some cats can't digest a diet that's all meat. My one cat had constipation, the other one didn't....
anyway...try pumpkin, try other things. I tried them too, but eventually I had to take my Peanut to the vet because it was just getting ridiculous and poop wasn't going anywhere, and i was told in the future to give her the fibre she needs because she can;t handle anything else. She ended up with constipation AND diarrhea because it was so clogged up and yet the pumpkin made a mess in there.
good luck with your kitten