I had a period this month but not that heavily. One day only a drop of…

I had a period this month but not that heavily. One day only a drop of blood and all still have signs of pregnancy. I had lower abdomen pain, nausea, diarrhea, back pain. The test showed a faint line, many tests done everywhere, they show a faint line. I don't know what to think. A week ago, I went for an ultrasound. The doctor said there is nothing visible.