First Choice best results are with in 3 days or as soon as possible. You had a stomach ache, did you have First Choice on a full or empty stomach? As for the diarrhea it could be a side effect from taking First Choice. As for the chance of pregnancy I"m not quite sure. Only way to find out is to stick with taking your birth control and take a pregnancy test in 2 weeks to make sure that First Choice was effective.
I agree, the morning after pill can make you sick. The chances of you being pregnant are pretty slim. The best thing to do is use a condom during your period if you have sex because not all women ovulate in the middle of the month. Were you on your period while on the antibiotics? If you are still on the antibiotics use a condom until you're finished taking them. You should be able to start back on the pill as usual.
seems as if your body was reacting to the morning after pill.