I volunteer at a crisis pregnancy center and we do pregnancy tests all the time.
One thing I learned, if you read the manual is that a postive test result followed by negative test results could mean an early pregnancy loss. EPL is very common, and most of the times it isn't even noticed. It would only be noticed if someone was testing a lot and happened to catch it.
I had the exact same thing happen to a friend and she said that she had a postive test followed by a negative test and the dr said that the egg was fertilized.
I really hope for your sake that it wasn't early pregnancy loss, and that you are pregnant.
If youd did have ERL, I am very sorry.
If you took a test and the control line didn't show properly, than the test probably is a dud, and I would suggest you retest.
Also, just one other tibit of information for you. One other thing I learned is that getting pregnant while using any form of birth control (condoms, hormonal, spermicides, IUD) can increase the chances of having EPL, miscarriage or birth defects.
If you got pregnant while using condoms, than most likely it was from sperm in the preejaculate (which are not the healthiest, normally one of those sperm would not be the one fertilizing the egg). Or if the condom breaks and the sperm travel through the latex and chemicals on the condom, that can affect "sperm health" as well.
I am really sorry you are having to go through all this.