Allergies

So my baby already has a cows milk protein allergy and he also reacted to oats. He’s already been referred to an allergy specialist. Wondering if anyone can shed any light on this newest reaction/ allergy or have had similar things happen.

My baby has had sweet potato probably about 20 times. He’s just now over 7 months old. About 3 weeks ago he had some vaccines that day & that night for supper he had some sweet potato and some bananas as well.. approximately 4 hours after eating he started vomiting a lot. It was very concerning and I called my local health line.. they said it’s unlikely to be caused by the vaccines and likely just a stomach bug so that’s all I thought about it ( and I really thought it was the vaccines because that was listed as a side effect). He hasn’t had sweet potato again untill a few nights ago.. 3.5 hours after eating he woke up from his sleep and started vomiting again! It went on for probably 1.5 hours.. after it stopped I waited about 30 mins then I tried to breastfeed him. He started vomiting again! So I was quite concerned he was going to get dehydrated.. I ended up spoon feeding him some breastmilk every 15 mins to get some fluids into him and he kept that down. After awhile I fed him and he was fine after that.

Question is… he has had sweet potato often and haven’t had a reaction up untill the past 2 times. I why all of a sudden is he reacting to it ? If he was allergic wouldn’t it if shown up initially when first trying it? I’m so confused.

I’m pretty concerned he’s only 7 months old and has had reactions to 3 things. Also 3 very different type of reactions. To see an allergy specialist where I live is crazy long and I can do nothing but just wait it out and not give it to him anymore. Super super stressed !