Am I feeding enough?

I'd stick with the mice for now, since it's working. Trying to switch him could make him stop all together.

It is amazing what some good online research will get you. Finding out now that the frozen mice I've been getting that are packaged as adults are closer to the size of a weanling, only around 17 grams. Where do you guys purchase your frozen mice or rats? I've been using the freezer at petsmart, probably not a good ideal, but I don't want to order a giant bag of them online cause I'm getting ready to move in a few weeks.

That would definitely explain why he's underweight. I have some mousers who would only eat one mouse a week, and are much, much bigger than your boy at the same age. (They're actually right on par for their age--mice work well up to a year old). But, those are adult mice...

If you're moving soon, and can't take anything frozen with you, I would stick with your current plan--feeding him a couple of those twice a week should give him about the same nutrition, and as long as he keeps taking them, it will be fine until after you move.

At that point, I'd buy a 6 month supply online. MUCH MUCH cheaper than you would pay getting them from a pet store, even with the high shipping cost factored in.
He can probably eat jumbo mice for a year, then you'll have to work on him to get him to take rats. It can be challenging to get some individual snakes to switch from mice to rats.

Once again, thanks for the help you guys. You are all a great resourse.

if he gets to a point where he doesn't eat everything you offer, most likely you're feeding him enough then. there is a big debate on power feeding. I would rather feed a little too much than not enough.