E.K.
Is your house on a pier and beam foundation? If so, the smell could be coming from under your house. The dirt under your house should be dry right now (in most cases). If the ground is wet or damp, you might want to find out why--make sure you don't have a plumbing leak (there's an indicator on the water meter near the street. If it's moving a lot and there isn't water on that you know of, you might have a plumbing leak) and make sure rain water drains away from your house. You might need to improve your gutters and/or ground water drainage.
If water isn't an issue, maybe you could seal the access to under your house better. I think odors can seep up from the ground under your house, especially when it's hot.
Good luck! I've dealt with (and am dealing with it now) this in both of the 1950's pier and beam homes we've lived in.