You can treat it at home and it should go away in 2-3 week. To treat it you should rinse the skin with soap and lukewarm water - you can also use rubbing alcohol - within the first hour. Make sure you wash whatever else might have poison ivy on it or you could get another rash later!
Then put on a cream for the next few days (Over the counter is fine!). You can take something like benadryl to help you sleep and help with the itching.
Soak in cool water baths to help with the itching and put a cool wet compress on the rash for 15-30 minutes a day.
If it gets really bad (lots of swelling, difficulty breath or swallowing) or you get blisters, you should call the doctor.