Clavamox is similar to Amoxicillin, but has increased spectrum of activity. The staph bacteria on dog skin can be resistant to regular amoxicillin. Diarrhea can be an unfortunate side effect to any antibiotic. Cephalexin is a great skin antibiotic that is not expensive. Clavamox is also a great skin antibiotic, but can be quite expensive in large dogs so is usually not what we try first. Diarrhea can be common with Clavamox, although some tolerate it fine. Giving the pills with food, can sometimes help. The class of antibiotics that probably has the least amount of GI side effects (and in fact is used in humans for IBS) are the fluroquinolones - Baytril, Cipro, Orbax, Zeniquin,etc. These too are great skin antibiotics, unfortunately, they are CONTRAINDICATED in young growing dogs as they can affect the cartilage (unless there is a potentially life threatening infection that is only susceptible to them). Antibacterial shampoos can also be a big help. The most important part of them is making sure they have sufficient contact time - i.e. 10 minutes -- and I know, this will seem like an eternity while you are bathing

Staph infections are very common in young dogs, especially short-haired dogs. It is typically recommended to treat superficial skin infections for 1 week beyond when you have any pustules, otherwise they often just come right back.
Note - 4 times per day seems quite frequent to me.... Cephalexin is usually dosed at 8-12 hour intervals in dogs.. .
Good luck with your pup!