Pregnancy question

Please help me understand this.... according to the first day of my last period I'm 6 weeks preg. But went in today and they didn't see anything on the transvaginal ultrasound.... So does that mean I'm less than 6 weeks pregnant? My last period was on July 13. But I know for a fact we didn't start trying until the 23-26.... So wouldn't that make me only 4 weeks pregnant? Also was worried about ectopic pregnancy so would they see that during a transvaginal ultrasound? I know it's rare, but I was diagnosed with cervisitis. I just hope I'm okay and so is baby. Doctor told me hcg levels are going up so that's good right?! Because I was having red bloody discharge early today when I wiped 3 different times...