I was also going to say that it could be an interaction of the foods with the antibiotic you are on.
Also, if the doctor suspects that your infection was in part caused by acid reflux, he could have told you to avoid the spicy and fatty foods to reduce reflux issues.
Take care and feel better.
Merry Christmas.
They're probably telling you to avoid spicy foods because the spiciness can further irritate your throat, making you feel worse.
If you're on antibiotics, some of those do have interactions with certain foods, so that could be another reason why you've been told to avoid certain food/drinks.