Eczema Treatment Care

My 7 mo. old son is getting these wierd red rashy bumps. He got one on his wrist about 3 weeks ago- started out as a whitish (lighter than his skin) tiny “bite” looking thing, with red area around the perimeter, and within minutes turned “harder”, more into a welt, and a red blistery thing appeared in the center. Within days, there was a cluster of red blistery things in the center, and it just looked horrible and irritated. There also appeared at the same time on the same hand, a smaller one which never really “blew up” like the other, just turned into a small red blister, and now has nearly faded. He ran no fever, and did not seem to notice it, did not try to scratch that I could see… We took him to his doc, they had 5 docs/nurses in the room and no one could tell what it was. They took a culture to see if it were viral, it came back negative. This thing got so ugly that 2 days late I took him to the ER. That doc mentioned flea bites or scabies- (yikes) but said there were things about it that did not fit with this diagnosis, like mom and dad did not have signs of it, and my cat and pomeranian are both on frontline plus, so have no fleas, and were rechecked to be certain- no signs of fleas. It is also much much large than a flea bite, and “hard” to the touch, and when you push around on it, the center will turn white as you are pushing, when you let go it is dark red again. And there was no way mom or dad had come into contact with scabies!! We even bombed the house with bug bombs just to be certain that nothing has bit him like a spider or something. We questioned food allergy, since he recently started solids… but the docs say no, that there would likely be a full body rash, or at least partial body rash, not just 1 or 2 welts. They gave him hydrocortisone which is helping it fade… Then this morning I saw the same thing begin ( I swear, right before my eyes, as I was bottle feeding him!!) on his right knee!!!! Same white dot with red around, and now it is becoming a hard welt again. I am so scared!!! Just don’t understand what it could be, and the docs do not seem to know either! The diagnosis on the paper at the ER was “contact dermatitis”… Some speculation was baby excema…anyone experience anything like this and might know what it could be? Or if any one has a baby with excema, how does this rash usually look when it begins to appear? I googled it, but can find no info. on what the initial sight of it is, if it is similar to my son’s mystery skin problem. Of course on Monday we will be taking him back to the doc, but if anyone has any info that may help me before then get an idea of what this could be, I would really appreciate it! (Sorry for the super long question!!) =)
Here is a pic, of the one today- my camera is not the best so it is hard to tell, but I will post it anyway.http://farm4.static.flickr.com/3306/3204…