The itchiness could be due to a number of things, including a yeast infection or another STD. It's important to call a doctor ASAP to get it taken care of, since left untreated, it probably won't go away on its own and may get worse.
While you're there, you can ask the doc for an STD screening, since you're at risk for STDs. Your partner should get tested, too.
Also, if it's been within 72 hrs (or even up to 5 days), you can take emergency contraception to prevent pregnancy. We have an article about it here:
So, get going to the doctor immediately! It's really important to address both the itching and your pregnancy risk right away.