Originally Posted by Doohickie

Yeah... you need to find out if all these flats have the same cause. The bike shop, or whoever changes the tube, needs to figure out where the leak is, and do something to prevent repeats. If it is due to running over glass or debris, an investment in flatproof tires is warranted. A less expensive (and slightly less effective) option is to get tire liners. It could be a problem with the rim itself though. There is a rim strip that covers the ends of the spokes to keep them from poking the tube. If the tape has a hole in it, it could be causing the flats. Or, if there is a sharp piece on the rim, it could be cutting the tube and as stated above it needs to be filed down.

To really get to the bottom of it, you're either going to have to have a bike shop thoroughly examine the rim and tire, or if you have a friend that knows anything about bikes, have them do it.