Assuming that the volume level is what may be expected in a small rehearsal room with acoustic drums, one of the more effective solutions may be somewhat counterintuitive: get a pair of ear-plugs.
Now, apart from reducing the overall volume reaching your ears (which is generally a good idea), ear-plugs will also filter out a lot of the more extreme frequencies, especially in the lower part of the spectrum. The resulting sound tends to be more defined, allowing you to hear what everyone (including yourself) is doing more clearly.
Another thing you might try is to swap places with someone - either the bass player or the second guitarist (if there is one). Chances are they are having a similar problem for exactly the same reasons and thus you both stand to benefit.
One thing I've done over the years in rehearsal situations was to position myself so I can train one ear on the amplifier (that means standing sideways to it) - the config being a half-stack on wheels, standing on the floor. Despite the fact that my ear was still somewhat above the main output cone of the speakers, it allowed me to hear better than if I had my back to the amp.
Lastly, you can try sitting down next to the amplifier (provided you have the room and can locate a stool or chair). This should improve matters somewhat.