[Marilize]

It looks like fleas to me. My female has the same reaction to fleas: she also gets bitten on her stomach and those bites become a little sore/blister because she scratches and bites them. Fleas don't bite me at all, so the best way for me to determine if we have a flea problem is to look at June's tummy.
To really know if she has fleas, comb her out with a flea comb and put any hair and debris that gets onto the comb on a paper towel. If there are tiny black specks of dirt, wet them... if it turns red or a rusty brown, it's flea dirt... and she has fleas.
I use Revolution for cats on my Yorkies to help with fleas and it works amazingly. It's a bit more expensive, but my vet recommended it after nothing else worked. I prefer to use natural remedies though, so I only use Revolution in extreme cases or during the flea season. Otherwise, I use eucalyptus oil in their shampoo and spray an eucalyptus-oil-and-water mixture all over the house.