#1. A) If you used a condom you have very little to worry about unless it broke (and I am sure that "oh shit the condom broke" would be in your summary if that was an issue) and if you used a condom you don't need to stress out over my following suggestions
#1. B) If she has been taking birth control she has to have been on it for a month before it will be effective. So there are 21 pills, so she takes all those and after the 1st pack is done it is considered effective. So if she was not already on birth control a month prior to you coming inside her, no, it will not help.
#2. Despite what Jennifer said, when ever you have unprotected sex you run the risk of pregnancy because an average is just that, an average, it doesn't guarantee that an egg won't be available on X days of the month to fertilize. You shouldn't assume that it's ok to not use a condom on the off chance that it's supposedly a good time, a doctor would have to do special tests on the girl to know the potential "best time" to avoid/get pregnant for certain.
and:
#3. If it has been less than 5 days, Plan B will still be effective, it is more effective the sooner you get to it. Plan B is the only thing that will act against pregnancy in these situations. Birth Control will not harm a baby. If it has been 6-7 days you could still try it but I would definitely monitor her period the next month and make sure she doesn't miss it, but make sure she gives it longer than usual (ex. getting pissed cause its a week late isn't helping, periods are a week late a lot, give it 2 weeks then get a test).
AND last but not least:
#4. If you guys are going to be having sex without condoms you guys absolutely need to be tested for STD's if you haven't been already and don't be afraid to see written verification of the results. AND AND AND the most important part: use the pill!! Unless you guys want a baby she should be on birth control. In any case, it's better to double up and use condoms AND birth control simultaneously. Better safe than sorry.
PM me if you need more