Reply: Part of the problem is that you are singing far from the microphone. That means your mic level has to be turned up more than if you were singing close to the mic, which increases feedback. If you can sing closer, the monitor sound can be louder before feedback occurs.
A monitor wedge speaker with a flatter frequency response will tend to sound better, and feed back less, than the monitor you are currently using. The JBL JRX112M is an excellent floor monitor selling for about $239-$279 street price.
The Crown CM-310A handheld mic, and the Crown CM-311A headworn mic, have better gain-before-feedback than most mics, which means you can turn up the monitor wedges louder with the Crown mics. That should help you hear yourself better. The CM-310A and CM-311A must be used with lips touching the mic grille because they are noise-cancelling mics: they cancel sounds at a distance.
Have you tried in-ear monitors? They will keep the drum sounds out of your ears, and will let you hear yourself as loud as necessary. If budget is a problem, use a headphone extension cable and some in-ear headphones.
Some bands enclose the drummer with clear Plexiglass panels to cut down on the drummer's stage volume. These panels are available commercially. Other bands have the drummer play electronic drums (such as Roland V-Drums) so that the drummer's volume can be controlled.