It does make it hard when you have very irregular periods
as you note. If your test is negative, but you still don't get your period, wait two days then re-take the test. If it is still negative you could see your doctor and possibly get a blood pregnancy test, which is more accurate. In general, the pregnancy test can become positive 10 days after pregnancy though every womans hormone
level of pregnancy (HCG) can be a little different at different stages of the pregnancy.