Not all pills work by stopping ovulation... in fact unless you do not have a period at all then your birth control does not work that way. Most shorten the ovulation time, or more commonly cause the mucus plug, which can be dissolved by ntbiotics to dissolve.
As illustrated I should say by your own posts.
Also if she was sick? I believe some over the counter cold medicines have the same affect as antbiotics on the plug
I'm still sticking with my original answer. Sperm lives on average 48-72 hours inside the vagina and it takes on average 3 months for full fertility to return after stopping the pill. Of course some women do fall pregnant whilst on the pill and by missing a pill but I still say that it is highly unlikely that you have any chance of being pregnant.
Some antibiotics reduce the effect of the pill, this does not mean that it is not working at all. You should continue to take the pill alongside the antibiotic unless advised not to by your GP.
The pill works by stopping ovulation, thickening of the mucus in the neck of the womb and also thins your womb lining. The chances of all three of these ceasing so quickly is remote as I am guessing that you had sex two or three days before you started the antibiotics by which case the sperm would've been dying if not already dead.
Having said that off course anything is possible. I have fallen pregnant whilst on the pill and i took it religiously!
Yes it is look up how long sperm stay active in the vagina, and how long it takes for the mucus plug near your cervix to dissolve.
It is not highly active but afterall timing is in the end, everything.
No. The antibiotics only make the pill in effective from when you start taking the antibiotocs. There is no way that it can backdate the ineffectivity to when before you started to taking the antibiotics.
Don't panic, you are fine providing you were taking your pill as instructed when you had intercourse. If you think that there is a chance that you could be pregnant I would suggest a home pregnancy test but from the information that you have given it sounds highly unlikely.