I am worried that i am possibly pregnant because i was taking an antibiotic while on birth control i had sexual intercourse 13 days ago but used a condom properly as a means of back up. i took a pregnancy test yesterday and the results came back negative.

There's : There's no way to know whether you are pregnant or not without the test. You can either take another home pregnancy test as long as it has been 5- 6 weeks since your last normal period, or you can go see your doctor and they can test you. A home pregnancy test is 97% accurate if taken a week or more after the missed period, so another negative test would help confirm that you are not pregnant. A blood test can tell if you are pregnant as soon as 7 days after conception and a doctor's urine pregnancy test can tell if you are pregnant around when you next period should come.

Too soon to test: If you miss your period by 4-5 days, do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless you get a period by then. Use first morning urine and follow the instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex. Get HPV vaccine