Don't know whether or not I'm pregnant??

I've taken three pregnancy tests so far. The first two were from the same box and the third one was from a different box and a different brand. The first test I took came back positive instantly, I went to the doctor the next day and she said that there is no sign of a baby anywhere on the ultrasound, she everything just looked normal. I re-tested a few days later, using the second test from the box, the line in the results window that indicate that I'm pregnant showed up, however, the control line was barely there. So I took a third test ( from a completely different brand) and I got the same thing, a solid line in the results window, but barely anything in the control window.

Does anyone know what's going on?

I should also mention that it's been a weeks since I took the first test and almost all of my pregnancy symptoms are gone.