Propane on BBQ used super fast?

I have a 2 burner Charbroil BBQ I have only had for about a month and grilled on it about 8 times average of 35min each time and already gone through 2 tanks of gas. I know propane goes further then this and Know! << I am not leaking gas or leaving the tank on. A couple nights ago it looked like the propane was empty then earlier today i fired it up and i had great flame and the gauge read full propane tonight i was going to grill and i got very small to no flame and the gauge read empty again i didn't leave the tank on. Can anyone tell me what can cause the propane to burn through this fast? Could i have a bad tank? What can cause this flux in power/ pressure? should i look into a better gas provider? I have no idea what im asking i just want my gas to go further