Have you read this yet?

I would start there

Also, the 100 degree basking spot... As far as I know BP's don't bask, and 100 degrees is too hot. Are you using a basking light? If so, I would suggest that you remove it. That is just my opinion though.

How are you measuring temps & humidity? Digital thermometers with probes? Humidity gauge with probe?

As far as feeding... the prey item shouldn't me much larger than the thickest part of your BP. If you have a scale, you could weigh his food - which should be approx 10-15% of your snakes weight (I believe - can someone confirm that for me, Its early and I'm still half asleep). You can also feed multiple prey items in one feeding if the prey size is too small.