Welcome @tejanajoy, I'm not sure if the post by @solco on the first page of this discussion where she shared the following link to an article that I think you might find helpful.
https://www.cureus.com/articles/69363-chronic-spontaneous-urticaria-after-covid-19-vaccine
@babsstruck, @solco14, @mallorymiller and others may have some suggestions or information to share with you from their experience. Here's an article I found on the topic that may be helpful.
-- Dermatographia: Causes and treatment of skin writing: https://www.medicalnewstoday.com/articles/319258

Have you considered calling your doctor to let them know the antihistamine is not helping as much as you thought it should?