the first thing I would recommed is: take off your tire and run your hand or a tire lever around on the inside of the tire - make sure there isn't something sticking through the tire that is puncturing the tube.

Here in New Mexico we have what is known as a "goat head" thorn - think of a goats head and you got it.....a 3 prong thorn that is very hard and very painful and Loves tires!!! On my MTB and commuter bike I run Slimed tubes. On the Peugeot I have kevlar tires (which they tell me won't work with goats heads but works great with glass) and Air-Loc tubes. On the Trek road bike I have a teflon strip on the inside of the tires and Air-Loc tubes. The only flat I've had so far was a pinch flat. I was also told by just about everyone that lives here, if you're running self-sealing tubes, leave the thorn in, the tube will seal itself around the thorn.