Are these all with the same tire? And is the tube puncture in the same place relative to the tire every time? If so, put on a different tire to solve the immediate problem and go riding. Assuming no more recurring flats, either toss the old tire or spend as much time as necessary with a bright light, glasses or magnifying glass, cotton balls, tweezer, etc. examining the old tire until you find the culprit, depending on how much life is left in the old tire and how much patience you have.

I once had a small bit of wire in my tire, the length was less than the thickness of the tire, so it did not poke thru when the tire was dismounted, it only poked the tube as the tire was inflated and working. I found it because I had 3 tubes all with a puncture in the same place that I could line up with the tire, so I knew where it had to be. Finally by pushing in from the outside of the tire I found it. Wouldn't have bothered except the tire was virtually new.