Bug bites that swelled up

Hi,

My wife and I have been getting some common bug bites on our legs maybe mosquitos or fleas etc. The bites on my leg are fine and just go away. For her they linger and turn red and swell up. My question is there anything that we can do to treat the infected area? Also, she has some scars that were left over from old bug bites what can she do to get rid of the scars, she tried maderma but that didn't clear it up. We would like to somehow stop these allergic reactions to a bug bite, since she used to not be this way. We went to a dermatolgist and all they can say is bug spray which doesn't work the bugs still bite, so is there any medicines or a shot that we can do to help with these allergic reactions?

I'm attaching a picture of the most recent bite that swelled up...she is treating it with some first aid bandages and rubbing alcohol...

Thanks,

Kevin