What Causes Late Periods After Having I-pill?

Me and my gf had unprotected sex on Aug 13 and within 14 hours time (on 14th morning) , she took ipill. She generally has regular periods on 1 st week of every month (this time also 3rd Aug, 10 days before unprotected sex), but after 7 days of taking ipill (on 21st Aug) she started bleeding (more than normal) and it lasted for 5 days (usually lasts 3-4 days). Is it normal period? Also she is supposed to get next period on 3rd of Sept, but till date (5th Sept)no sign. Also her breasts also got a bit fatty. Is she pregnent or this is the effect of ipill? How long should she wait for next period? Or should go for pregnancy test? Both worried