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Pills are always started either on the first day of periods or the first Sunday after periods as it makes sure that you are not pregnant and secondly to maintain the regular cycles and hormonal levels.It is better to start once you have the periods.Since you have been on the antibiotics they would decrease the efficiacy of pills depending on the dose,duration and composition.
Consider visiting a Gynaecologist who after evaluation of the antibiotics can advise you regarding the pill use and its effect.
Take Care!