My boyfriend and I had sex a day or two before my planned period [so I was already feeling pre-period symptoms: sore/swollen breasts and fatigue]. He had a condom on. After he ejaculated we found out that the condom had broke. We got planB pills the next morning and I took them as directed and it said that I should either have my period at the usual time it comes or at most a week after the time it should come. It's only been two to three days after my planned period and four days before the "week delayed" period that planB had suggested would happen. I can't tell if it's because my period is going to come or if I'm pregnant because my breasts still feel sore/swollen and I still feel tired. I don`t have any other pregnancy symptoms other than the delayed period [which may or may not be due to planB] and the sore/swollen breasts [which may or may not be pre-period symptoms]. What should I do now to know whether I am pregnant?

The best way to know is to take a pregnancy test, but you normally need to wait 2-3 weeks after the unprotected sex to get a reliable result. Any sooner may give a false negative.

There are a lot of things which will give you tender breasts and tiredness, including PMS. Four days is too early to be showing pregnancy symptoms.