honestly you sound like you've tried everything. i'm not sure the problem is your dog anymore so much as it is your house. when you have one flea chances are you literally have thousands! i've been there twice. fleas ended up in my garage and my animals were NEVER in my garage. my advice is get professionals to come bomb your house. while they are doing this take your pets to the vet and have them dipped and just a little fyi i also recommend putting flea powder in your car and doing A LOT of laundry in hott water. i know it sounds extreme but when you leave two fleas behind in a month the same problem will occur with thousands.
good luck!
barbie and kira