My allergy doctor told me 3 weeks.
If ypu have an Anahylactic reaction, whether it be mild or severe (as far as stomach cramps or breathing difficulty, swelling etc..) my hospital told me that it can re-occur at any time within the next 3 days. For no apparent reason 😕 That is why (in Australia), they give you antihistamines and steroids for 3 days after Anaphylaxis.
I just asked the same question. I am at end of week one and still feel awful if I don't have prednisone in my system.
Mine can last up to 8 weeks but it depends how bad I am. Usually the normal is 3 weeks. 8-))
It all depends on your body. I can have reactions up to 8 weeks. I use Benadryl the tablets because the gel form is made from soy, and I am allergic. It helps slow down the reactions but it also puts you to sleep. I would talk to your doctor about it.