Do a nearly professional system check:
Make a manometer - get a yard stick, some clear tubing and rubber bands. Strap the tubing to the yard stick and put water in it.
Dismount a stove burner.
Plug the tubing on the jet - the brass part that sticks out when the burner is removed.
Turn the gas on.
Turn that burner on.
The water should shift so the difference in levels is about 11".
Turn the gas off at the tank.
Walk away and don't come back for a long time.
Are the water columns still where they were?
If yes, you don't have a leak.
If no, find the leak.
Matt