What do I do to stop the itching of my poison ivy?

Calamine lotion! I always keep a bottle nearby, as I randomly get idiopathic rashes. It's only a few dollars at the store. You just need to wash the rash and pat it dry before rubbing it on your skin. It's specially made for contact dermatitis so it dries the oozing poison and stops the itch. As for preventing it, since you're aware of your allergy you need to be aware where you're going to not run into it. If you do go out in the weeds or woods or wherever it is, make sure you wash the clothes you were wearing as soon as possible and wash your hands! If your doctor hasn't given you any medications for it, which I find odd, then you just have to use the preventative method to stay away.