Must be a leak
A tank on my boat will last 4 months or more. We use the boat (Legend 37) on weekends and also a two week summer cruise. We have no oven and use the propane grill a lot. Also, a full tank should contain 2250 psi. Check around with gas companies who may fill them. Sometimes companies who fill welding tanks, etc have those contacts. A fill at Corp Brothers in Providence costs about $15.00.Another thing we do is to shut off the tank valve and burn off the excess between uses. This is more a safety consideration, but if you have a leak, this will let you know. Keep an eye on the psi when you aren't using the stove/oven. If the psi drops, you know, for sure, taht you have a leak.