Poor Baby!

This is what our little man's back looked like when I got in up from his nap yesterday. He was full of hives. A couple days ago, I gave him mandarin oranges for the first time. He woke up from his nap with a red rash (not like this one) all over his entire chest. I figured it was from the oranges, but I also looked at the stage 2 baby food I gave him for lunch and it contained egg whites. I know that you're not supposed to give a baby egg whites until they are one, so then I thought it was from eggs. However, I think I have already given him that flavor before and he didn't have a problem with it (but I doubt there is much egg in it anyway.)
Anyway, yesterday I gave him a broccoli/cheese baby food (which he loved) for lunch and this is the rash he had that afternoon. So then I was thinking he's allergic to broccoli or onion powder since they were also in stage 2 food he ate a couple days ago. So last night, I only gave him his oatmeal and sweet potatoes and he had his formula. This AM, he had the same welts as in the picture, but they were scattered around his back, arms and legs like mosquito bites.
Both times, it cleared right up with hydrocortisone cream and he was acting fine (except for his "party" in our bed from 1-3:30 this AM....wide awake, ready to go. I was so annoyed since I had just gotten home from work and was so tired. It never occurred to me that he was probably itching like crazy and couldn't sleep because he was covered in hives. Once again, sign me up for Mother of the Year...)
I was going to try and wait it out since I still thought it was from something he ate, until he woke up from his AM nap and his face was covered with welts. His left eye was almost swelled shut, so I called the peds office and off we went. The on call ped is sure that he's having a delayed allergic reaction to the Amoxicillin he was on for his ear infection. Even though the hives didn't show up until day 9 out of 10 of his course. He said that food allergies show up almost immediately after eating and will go away within a day. And since his keep "popping up" he thinks it's from the medication. (If it is a food allergy, he thinks it would be from the oranges and wants me to try them again later to make sure) He said that this med typically stays in the system for about 72 hours, so he should be better by tomorrow night. In the mean time we have to give him Benadryl around the clock to keep the hives away (which has been working, and thankfully he doesn't get "crazy hyper" from Benedryl like some kids do). I waited a little longer to give it to him tonight so he could have it right before bed and he started getting spots again...poor baby!
Hopefully he'll be in the clear after tomorrow and we can blame it on the med and not food. I am praying that is the case. I know how terrible food allergies can be!