I have work a clinic, as a doctor (not an immunologist), that was involved in a desensitisation program for jack jumper ants and to a lesser extent bees and wasps. It's only available for people with anaphylatic reactions. I'm not sure if tick desensitisation programs exist. The immunologist you are seeing will be able to answer that.
I'll generalise to what I know about anaphylaxis with jack jumper allergies and what I discussed with patients everyday.
We don't don't know why people develop anaphylaxis. It may occur after one bite or fifty.
The severity of the reaction is not related to the amount of toxin, there tends to be a threshold and once that it reached anaphylaxis occurs. Subsequent reactions are likely to be about the same severity with a small chance of having a more severe reaction.
As a general rule the only way to treat anaphylaxis is with adrenaline. (Please don't use this as medical advise - adrenaline isn't always needed, its use needs to be put into clinic context and a medical practitioner will be able to instruct you on that.)
Antihistamines and steroids (prednisolone) will not alter the course of reaction, they may help slightly with symptoms relief.
Carrying an epipen is advised and calling an ambulance is an absolutely appropriate course of action.
