Well yes antibiotics can definitely mess up your pregnancy test. My sister in law had a similar situation. She had been taking antibiotics and could not realize she was pregnant. Then she went to the doctor and finally took all the tests like ultrasounds, urine and blood tests and the doctor finally came up with the pregnancy. You must visit the doctor as soon as possible as if it is a pregnancy, the antibiotics can harm the baby.
Ever watch the show I didn't know I was pregnant? Well, apparently antibiotics can cause your birth control pill to become much less effective, thus a higher chance for you to get pregnant without realizing you were at a higher risk. But a false negative result no, though they are fairly common. Give it a couple days and retest if you still haven't gotten your period. Or the doctor can always do a blood test.