Could be the thorns from the stickers?

If I was getting minuscule puncture flats, I would probably get some liquid sealant for inside the tubes. I can feel the difference in rolling resistance betwen ordinary brands of road tires; buying completely puncture proof ones must really be a drag, pun intended. The rubber may be thicker or harder and the flat preventative also adds thickness and mass to the tire.

I used to ride a 3 speed with unprotected department store tires in the city of Chicago and it was mostly fine, so I second the suggestion to ensure that you're not underinflating or using too narrow a tire for your rim. I currently find that most any tire which is listed as puncture resistant like Nashbar Primas works fine.