We recently had a new undermount kitchen sink installed and the drain hole is in the center towards the back of the bottom of the sink. When we went to re-hook up the garbage disposal, we realized that the garbage disposal is now right up against the drain pipe going into the wall. There is no room to hook up the trap or connect the disposal to the drain. Do we need to reroute the drain pipe, or is there something else that we can do?

Without a picture this is a tough one, but you could simply lower the drain hole location. Hopefully, your waste line is PVC so it will be relatively easy to do. If it's still not possible, you will have to re route to the side. Just remember when you do, always keep a slight pitch of at least 1/4 inch per running foot.

Thank you for the info. The drain pipe in the wall is not PVC, but our we have a flexible union on that connects to the PVC trap. How do we go about lowering our drain hole?

I hate to rain on everybodys parade but to lower the stub out would involve removing the sink and cabinet, tearing into the wall allthe way down to the stack and cut the stack twice to lower the sanitary tee that picks up the sink. This would not only involve the plumbers but drywallers, painters and cabinet men to reset the cabinet. It's just not as simple as dropping the stubout with a couple of elbows.
Turn the disposal until it's pointing mostly to the front to get it away from the stubout. Now cut the trap out and repipe to the disposal if you have the elevation to do so. Charging a sink means charging the drainage also. Good luck, Tom

Yes, turn the disposal, I should have mentioned it but I figured you already tried that.
If that doesn't work and you are really attached to your disposal, do you feel comfortable doing any or all of these yourself?
-Removing the drywall with a hand saw
-Cutting the drainage pipe with a reciproting saw whether it be galvanized steel, cast iron, etc..
-Drilling holes in the framing to re route the drain line if you need to
-Fastening a flexible union to the end that you cut and assembling, priming, and gluing PVC, ensuring you have a proper P-Trap to the disposal
-Installing new drywall, in this case Green board, and finishing it.

You could save $$ if you can do any or all of this yourself. But if this seems overwhelming the skinnier/shorter the plumber, the better to minimize the items needed to be moved out of the way.