I really don’t think you can have an allergy from the black seeds. In this article: Nigella Sativa, the black seeds, can cure every disease. Come on… I have also written about its antihistaminic powers. In fact, there was a funny episode, in 2010, with Nestle, which try to get a patent on the use of Nigella Sativa to “prevent food allergies” in its cereals. Like an exclusive right to use the black seeds in their products! To own the black seeds. Of course, it’s hilarious and the authorities probably thought the same, as they refused them the patent.
But the idea remains. The black seeds are really efficient in fighting allergies. Search for the source of your allergy in a different part.