Vicki, I had the same problem with my property. It could be that one of your under ground pipes is broken. Your septic needs to be pumped. Your soil make have alot of clay and the soil is not percolating or the worse yet you may need a new leech field. And if you have poor soil percolation you may need a raised bed leech field. I needed a new leech field that was a raised bed on a home I bought that had both a dye test and the septic pumped. Needles to say I though a septic system was supposed to last about 30 years if pumped regularly. But the septic system I had the soil didn't percolate because it had so much clay. Get a septic guy and first try pumping and they have a detector to check for leaks or cracked pipes. The they take like a dowl rod and put in the soil in your yard and if it comes out blck and looks like sewage the soil is saturated and that will be the clue. Good luck. I took waht I though where all the precautions before buying the house with a inspection for the septic but I had to get a new leech field. It is expensive but the odor was gone. Come to find out from the neighbors that it was a problem with alot of them and they had to end up with raised septic beds also. The house was only seven years old and when we bought it and we had that problem under the same curcumstances.