After eating some porridge i got a headache, so i'm wondering whether i'm allergic to oats?

Possible, so try...: It is possible the porridge caused your headache, but also possible this was just a coincidence. Avoid oats for at least a week and try again; if you get a headache again then try avoiding. Also, if sensitive to oats explore it you might have a gluten sensitivity, as gluten can cause headaches in some. While pure oats don't have gluten, most oats have small amounts due to how they are processed.