My DH swears that he had it more than once and from what I read it is rare but often genetic that you can have it more than once. Piriton is great for the itching and so are bicarbonate of soda baths - although I am sure you know about all of that having been through it three times already! Hope they are not too poorly with it
Yep you can get it more than once...some people (rare) don't get an immunity to it. Some people get it twice an no more (only mild exposure 1st time) others never become immune.
I've never developed an immunity and this is now a problem as I'm on immuno suppressants for something else, which makes it very dangerous for me to be exposed to it. (i've had my 3yr old immunised against it to reduce my chances of exposure)
Dr's can check whether or not you have developed immunity but usually don't because in most people it is an unpleasant but not life threatening condition. So they will probably never be tested unless its for something else. Sorry to hear yours seem to be unlucky, hope it goes away soon