Should the level of water in my septic tank rise when it rains a lot?

Well, you should have it pumped and checked to make sure that everything is ok. We had the same problem and yes water from rain will go in there. The problem is most likely what you said... the leach fields are drenched and there is no where for the water to go. If there has been some construction in your area or a bunch of trees were cut down this could be your problem as well. The leach fields are being stripped away and are completely useless when there is not enough room for the water to go where it needs to. We found that by planting a few trees in the yard and starting a small garden it helps (tomatos love to live by a septic tank). However, you should have it checked to make sure that there are not cracks and that the places where the water leaves the tank are not clogged. We are getting onto public sewers soon (it is just becoming available to us) so we are trying to make this tank last until they have the plant up and running because they will charge us to connect to the main lines. Good luck, you should be able to let all of your water go out there... so something is wrong and calling in a service man may be your best bet.