PA system question

When I practice with my band our PA feeds back a lot.The room is a small one that lends itself to microphonic feedback.We can't necessarily turn down our amps because our drummer doesn't really posess the dynamic skill to play softly ALL the time so we have to crank the volume up. We really don't play as loud as you think so my question is as follows:
What can I do to reduce the feedback without turning down?
Do notch filtering units work well when mics are in close proximity to PA speakers? Do I have to buy a stronger power amp (because the one I have now is being pushed close to its limit)? Will a stronger amp feedback like a weaker one but at a lower volume setting?
Any suggestions other than replacing the drummer or getting a bigger space to practice in?

try tweaking the EQ, usually, turning the highs down works good on feedback