time taken for symptoms to appear

Sounds like you may have a seafood allergy.  You should probably see you dr. when you can and find out if you are really allergic to seafood because if you are you need to avoid it.  You can get a very bad reaction especially when your throat closes up.  So please be carful with this and see your dr as soon as possible. Take care.

Aurora

An allergic reaction can have two parts - the early part (or "early phase") is the throat itching, etc. that you got within an hour or two of eating the prawns. Antihistamines generally help control this part of the reaction. The second part of the reaction (or "late phase") can have the same or different symptoms as the early reaction, but because it can occur up to 2 days later, you never know when it will hit...and sometimes it can re-occur more than once. Steroids or other anti-eosinophil medications are usually needed to control the late phase in those who have more severe symptoms. Recommend you see a doctor and discuss this with him/her, and also ask for a prescription for an EpiPen since your symptoms are suggestive of potential anaphylaxis (which can be very serious or even deadly). Good luck,