I had a similar problem recently especially when coming through the door and in or near the garage door and surrounding areas. It turned out that the mix my husband uses for the lawn mower (this blue liquid) can't think of the name right now was causing all the problem. My husband stored it NEAR the gas he uses along with the mower all in the same spot under in the garage which is under our stairs. Apparently, the mix of this blue liquid and the gas being together (even though they were in separate containers) caused the reaction in the air which was circulating throughout our home. Don't ask how I even figured it out :-) I made him remove these items from the garage and place them separately and apart from each other (one bottle in the back of the house outdoors and the other in the front) and we immediately smelled the difference within hours inside the house. This had never happened before and we don't know why it suddenly caused such an odor but we haven't smelled any odors like again. Good luck to you!