You can carry out a pregnancy test from the first day of a missed period. Tests that are done earlier than this may not be accurate.
If the test is positive, this means you are pregnant. All pregnancy tests, when carried out correctly and at the right time, are reliable. This includes tests that you buy from the pharmacy or supermarket to do yourself.
If you don’t have regular periods, and the test is negative, you should repeat the test at least three weeks (21 days) from the last time that you had unprotected sex.