Sorry, can't really give you much insight from a piloting point of view.
I suspect the only people who can give you a definative answer are the CAA.
It'd be helpful if you could get your ducks lines up for them before you contact them.
I should imagine they would be interested in exactly what happened initially. "Allergy" is a term banded about, but could mean anything from getting a rash to collapse and respiratory failure.. I should imaging something serious has gone on here, and i suspect at some time you've seen an immuniologist, if you've been prescribed an epi-pen.
They would also be interested in what's happened since. Any further episodes, and what was the form ?
It's be useful if you could get a copy of the clinic letter from your GP also. The blod result is probably not as important but worh getting.
Good luck.