Have not read through all replies, so apologies if I am going to repeat someone's opinions
1. Guests do use more of everything, there is not way to force them not to - due to various reasons
2. In my house rules I put: "Please concerve electricity as its price is sky high now and usage is measured after each guest's departure and you WILL be charged if bill is much higher than average
3. Price of gas does not stay the same - here is a weekly chart that might explain why you saw the spike
Like previous poster suggested - leaving only 2-3 pods for guests' use is a good idea