thanks for using health care magic.
testing after the date of expected menses in a sexually active women is over 80% sensitive in diagnosing pregnancy. With a positive test and with a missed period, pregnancy is the diagnosis.
Concerning, the last series of pregnancy tests
being positive and later negative, a logical explanation could be that you had a missed abortion
(if considering that all both results were correct with no error) and by the time you took the second test that was negative, B-HCG
levels ( hormone use to diagnose pregnancy and secreted by the developing embryo) were already low to be detected. B-HCG levels typically fall within 3 weeks following termination of pregnancy. Also, the possibility of having one of the test being a faulty result cannot also be left out.
However, the present situation is what is in question. You could do an endovaginal ultrasound
to have a visual proof of pregnancy or repeat pregnancy test.
Concerning the pregnancy symptoms, it is possible not to have symptoms at this early age with only a missing period indicating pregnancy.
Best regards and hope this helps you.