once your allergic to something its for life. its better you avoid taking soy again in any form. if you are certain soy is the one which is causing stomach pain and vomiting
than you do not need to do any test for allergy
, any food item allergy you have to avoid in any form.also take antihistamine tablets those will give you relief and you will not feel sleepy also, like citrizine etc . benadryl
takes arround 2-3 days to leave your system.do not worry about side effects of antihistamine just take correct dose. and do not drive after taking antihistamine.