I just take a small sponge, dip it in water and make a few passes on the grain side of the leather until it looks damp. Then let it sit for maybe 15-20 minutes and start. Normally this works well for me. As I work and leather seems to be getting too dry, I lightly make a pas with a damp sponge (not soaking wet) and wait a minute or two and then resume.
Sounds to me like you are just getting the leather too saturated. Try this on a test piece and see how it works for you.