How long does it take to be sure i'm not going to have anaphylactic shock? i have had it in the past and now having allergic reaction.

Go to hospital now: It's not worth risk of having someone find you unconscious or worse yet, dead. So if you've had an anaphylactic reaction in past, go to hospital now. Have someone drive you (or call 911 equivalent in new zealand) so you don't inadvertently pass out & crash, potentially injuring someone else. Once all is well, ask your doc for Epipen (epinephrine) (or kiwi equivalent). Keep 2 on your person, just in case.

Can't tell: Until you can identify the cause, it can come on at any time - fast and furious. Even if you have identify the cause, inadvertent exposure to the food etc may still happen. Be sure to carry an adrenaline kit with you at all times.

Is it anaphylaxis?: You tell us that you had an anaphylactic reaction, but experience has shown that not every person who claims to have undergone such a reaction actually had it. Until proven otherwise, you had anaphylaxis and need to carry self-injectable epinephrine. If you have a reaction at this time, have someone else drive you to an urgent care/er. Most important: see a board-certified allergist asap!