Can Antibiotics affect a pregnancy test?

No. They can make the birth control pill less effective, but they shouldn't have any effect on a pregnancy test.

The main problem with home pregnancy tests is that people test too soon, or don't test correctly. Most people don't use first morning urine, and they test a few days after a missed period. If those tests are negative you're not in the clear, because of human error.

They should have no effect on the test.

Tell us what is happening in your testing ?