Hi My Name Is Ali I Am 24 Years Old.3

Hi my name is ali I am 24 years old.3 days ago I eat medicine for alergi name Atarax after 10 mints my whole body react to it so much I was shaking freezing ,,, now I am bit better but I am feeling so weak have little pain in my haert side and my heart beat is going fast and slow.can you plz kinrly inform what should I do and why this is like that.
Hope for best