First and foremost - it is NEVER "safe" to have unprotected sex. The Pill is not 100% effective, and it will never protect you from STI's, AIDS/HIV etc.
You will need to take the first blister pack of pills - 1 month - to be protected. Your doctor has taken into account your antibiotic use (which affects the efficacy of the pill) in his calculations. The month-long cycle of pills is made up of Sugar Pills and the Hormone Pills. The sugar pills are the ones you take when you have your period, the rest you take one a day, at EXACTLY the SAME time of day. If you miss one, you will need to again complete a full month properly before you are protected again.
Again, the Pill is NOT 100% effective and it is never safe to have unprotected sex.