Stage monitor feedback

[Rosenfelder]

I am trying to use two or three Galaxy PA6S monitors as stage monitors, for small venues.
I have not had time to learn how to set them up before actual gigs, so I have been trying to de-bug my technique, by setting them up in my living room. The room is about 12' by 19', with wood floor, a large area rug, and several windows. I have tried SM58s, SM57s, or 55SH mics. I positioned the PA6Ss directly behind the mics. I can barely turn up the volume (to the second mark on the volume dial) before I get feedback. I've tried adding in an ART 231 EQ, which lets me get slightly more volume before feedback. I get a lot of hot frequencies, and basically end up turning five or six adjoining sliders down, in two or three areas of the EQ. By low volume, I mean that the direct sound of voice or guitar is louder than the sound coming out of the monitor, and therefore not useful.
Question: Is this relatively small room (with reflections) what is making the speakers so sensitive to feedback?
I am using a Yamaha mixer with two Aux sends. There are several points where the signal chain can be turned up (or down), including the first gain pot on the mixer, the aux send pot, the EQ controls, and the monitor volume control.
Am I wasting my time trying to set this up, and teach myself how to do it, in a 'small' room, and should I just experiment out doors, or in church, function hall etc?
Or am I missing something, in the gain structure, etc.?
I have searched the web, reference books, and manuals, but they make it sound too simple.
Any help would be appreciated.
J.R.