Years ago, I used to play on the street, 8-10 hours at a stretch on weekends, and only broke 2-3 strings per week (i.e., per 40 hours of performance, not counting woodshedding, partying, etc.). Plus which, I've always used picks (two metal fingerpicks plus a plastic thumbpick) and played hard enough to scratch the bejeesus out of my guitar -- not at all easy on the strings. I've always used bronze medium-guage, admittedly not the most fragile.
But two nights out of your two middle strings (G and D)? You must *really* be pounding the crap out of that poor gitfiddle!