No method of birth control is 100% effective.
Condoms are very good for protecting against STDs. Luckily you used one. If this was only a one-off time, there's a very good chance you will not have gotten pregnant.
Pregnancy tests can be taken sometimes as soon as the first day of your missed period. Look for one that says that. A good brand is First Response.
If you do get your period, you can not take the pregnancy test as your hormone levels will be off and it will not give a true reading.
Just because you get your period doesn't mean you aren't pregnant. My sister-in-law had her period up until her fifth month of pregnancy. If you're not sure, go to a clinic and have a blood test done, that's the only way to be sure. If you go to your family doctor, they will probably only do a urinalysis (just like the drugstore pregnancy tests).
My sister-in-law was using condoms and the birth control pill, and 2 months into dating she got pregnant. My nephew was born one week before her and her boyfriend's one year anniversary together. And she's a nurse. So as you can see, no method is 100%, even two methods aren't 100%.
If you get into a long term relationship, or even if you aren't but you think there's a chance you will be having sex in the future, I would go to your doctor or the local Family Health planning clinic and get the Birth Control Pill. Remember you have to be on it a month for it to be effective. That, PLUS condoms (always with the condoms! You just NEVER know and an STD could ruin your life!) are about as effective as you're going to get with birth control.
If money is an issue, your OB/GYN will be able to give you samples of the Pill until you can pay for it yourself. Same with the family planning clinics, there might be a nominal fee of 20 dollars for 3 months worth but it is money well spent, your body (and the chance of a baby) is not something you should be messing with!!!
Good luck hun and please keep us posted!!!!