I'm leaning towards some kind of obstruction, kink, pinhole leak, etc. Are there bubbles in the entire line, or is it happening at the faucet? A week at 45°F probably isn't enough time to over-carbonate using only head pressure, and after a dozen pints the head pressure should have dropped to essentially what the regulator's set at. Are you sure it's at 5 psi? Vent the regulator and double-check.
5 psi is really low for a serving pressure, too, but that probably isn't related.