Is it worth taking antihistamine again 36 hours after a hornet sting?

I was stung early yesterday morning and put afterbite ammonia on it but by the afternoon my ankle had swollen so much I could not move my ankle. I took antihistamine then. Today it is still swollen, red and hot but moving more easily. My friend advised me to elevate my leg but with two dogs and a child and a house to look after, I admit I have not done this and now it is stinging and itching and feels very hot and tight. I took the antihistamine at this time yesterday. Is it worth taking it again today or is too late to do any good?