They will probably give you steroids which generally reduce the inflammation, swelling and intolerable itching right away. Our experience with steroids for poison oak is that as soon as you finish the prescription (and it does have side effects for a lot of people) the poison oak came right back, the same day the meds were stopped, in the exact places it was before. Happened a couple of times.
So be prepared, you may still have to deal with it after the meds, if they give you steroids.
Here's a longterm possible solution that has worked for 2 people I know - drink goat's milk from a goat that has been fed poison oak (or ivy). Goats love it, it's everywhere (!) and after 6 months to a year of drinking said milk regularly, you either won't get the rash at all or your reaction will be minimal.
Some people have luck with homeopathic remedies for it too.
That's exactly what they gave me and said to make sure I take the full dose or it could come back. My face took the brunt of it -- can't even look in the mirror