I posted this previously and I will add it here again, its a good read.
also forgot to mention, if you are using scented litter change that to unscented...let us know how you make out ok.
http://healthypets.mercola.com/sites/healthypets/archive/2009/12/23/environmental-allergies-and-your-pet.aspx
good for you for reading all the posts, there are many on this site that deal with this problem, its very unlikely the culprit is stress...more likely an allergy. remember kitty doesn't have to have fleas for a 'flea bite allergy' to spring up it only takes ONE bite.
the reason is usually always allergy's. to the food, the environment or to fleas.
first of all STOP dry food, its loaded with chemicals and preservatives. I will give you a site that names good commercial can foods that are avail...also stop using all chemicals in your home, candles/cleaners etc.
rather than sardines in olive oil, I would get a good quality Omega 3 vitamin to add to the food (or give orally if he wont' eat the food its in)..the best one on the market is Krill Oil. NOW Foods brand is one of the best, for cats it has to be free of soy and preservatives. I can tell you where to buy it if you can't find it in your local health store.
post again if we can help more. good luck
http://www.catinfo.org/?link=cannedfoods