Let's say you're allergic to peanuts. And you eat them. How long till the allergy symptoms start reacting and how do you know if you're allergic to something you eat? I have this weird problem when I swallow. It's difficult to swallow actually. I let a week go by to see what happens but nothing. so I'm guessing it could be allergy. I'm not allergic to anything and NO ONE in my family is allergic to anything so I really don't know how all allergies work.
It will vary depending on the severity of the allergy. It can be extremely quick, as in just a few minutes, but it can also have a more delayed reaction time.
If it's difficult for you to swallow in general and it doesn't reoccur after you've eaten something several times, then it's most likely not an allergy.