Your gas mask is broken, I had the same problem when I had to protect Bourbon...
Search the dead bodies for a gas mask..
Im not sure that's it.. I have the same issue.. (i had 23 filters, and the watch was in the red) i press g once, and it does an animation of him changing the filter, yet the clock never resets, and my guy is breathing heavly and i've also found a new mask a few times with no changes..also i've noticed that the number of filters goes down sometimes with out me having to do anything, the only settings i have on are unlim ammo/money and every now and then no reload.. I also can't seem to buy a few of the guns, anyone know if they are unlocked later?