Firestorm
Pedant
Do not leave the house without your Epi-pen EVER. It should really have all been explained to you, but in the case of an allergic reaction, then the epi-pen should be administered - you hold it like a dagger pointing at the outside of your thigh and thrust it against your thigh (not hard enough to bruise, but hard enough to feel) and hold it there for a count (I'd have to check how long, think it's 20), it should give a "click" to show it's worked. This administers adrenaline directly into your blood stream. Once used it needs replacing - if you ask, you should be able to have a practise with some "empty" ones, but Pubey is right - speak to your GP.
just to add, rub the area immediately afterwards to assist in the dissipation
Regularly check the unused ones to make sure they are not out of date.
To be honest , it may be of help , if god forbid you collapse in public, to wear a bracelet identifying the problem. It would certainly assist any first aiders etc who may well be able to look for the epi pen a bit quicker.
The symptoms do sound a bit anaphylactic to me
http://en.wikipedia.org/wiki/Anaphylaxis
http://www.nhs.uk/Conditions/Anaphylaxis/Pages/Introduction.aspx
They may not know what causes it yet, I would suggest that there may be a number of "scratch" tests on the horizon