[Ryland]

You shouldn't have such a hard time tracking this down, you might try calling an electrition and seeing if they have a clamp type amp meter that they can come and test each breaker to tell you what it's load is.
It does sound like it's your water heater, maybe you have a water leak? do you get a water bill for your apartment as well? your water heater should keep water hot for 4-5 hours after it's turned off, if it's cold within an hour or so then you have a hot water leak and your water heater is basically always on.