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It is better to use additional protection during the withdrawal bleeding time to avoid chances of infections and also increase the protection (especially if this was your first birth control pill pack use). Most of the hormonal contraceptives start giving you effective protection after about 2-3 weeks of regular use, so you can resume having unprotected intercourse after getting started on second birth control pill pack. But if you are worried about pregnancy and are not prepared for pregnancy, always use back-up protection while having intercourse for additional protection against pregnancy (as no single birth control measure gives you 100% protection).
Take care.