How Soon Can I Expect Periods After Taking Cerazette?

HI, i recently stopped takin cerezette aftr havin a coil removed.. i only took it for 3 weeks and ive been stopped taking it for 7 days.. i feel pregnant but know this is a side effect as i have had negative results when testing.. im keen to try for a baby but would really like to know how soon to expect my period?? my last cycle was 6th march (start date) im worried about it as im always regular (29 days) please help