How old is your bike? I had a similar problem with a very old road bike I had. I'd get a flat every couple of times I did a ride. Turned out the inside of the w

How old is your bike? I had a similar problem with a very old road bike I had. I'd get a flat every couple of times I did a ride. Turned out the inside of the wheels had gotten corroded, creating lots of sharp edges and the result was that it took _very_ little to puncture the tube. New wheels fixed it for me, but a cheaper solution that might work (didn't for me, but could) is tube tape to help protect the tubes from the wheels.