Pinch flats. Try nflating the inner tube SLIGHTLY when you install the tire (a couple of pump strokes, even less). Then KNEAD the tire to MAKE SURE THE TUBE IS NOT PINCHED BETWEEN THE TIRE BEAD AND THE RIM. You do this with a backward rolling motion on the tire, also pull UP a bit while doing this to allow the tube to escape and get inside the tire casing if it happens to be slightly pinched. Do this all the way around the rim. Also: when snapping the tire bead onto the rim finish off OPPOSITE the valve, not near the valve.

I think that is your problem, pinch flats.