Can taking antibiotics cause a delay in menstruation (amoxicillin and ceftin for bronchitis, followed by a single dose of Canesten)?

Yes, taking antibiotics can potentially cause a delay in menstrual periods. It is possible to have a negative pregnancy test result even with a delay of three days, as the sensitivity of the test can sometimes result in a false negative. If your period still hasn't started, it is recommended to take another pregnancy test in a few days.