Could the Dr. be wrong?

I have had 2 ectopic pregnancy with the result of the Dr. removing one of my fallopian tubes. The Dr. has told me to take regular pregnancy tests monthly and to come in right away if I find out I am pregnant. Well, this month, I should have started my period on Friday, April 22, but instead I started on Tuesday April 19th with no cramping at all, which I usually have super bad cramps. I took a pregnancy test anyway and it was negative. I just thought my period had come a few days early. I had a super heavy period as well. Well on Monday, April 25th, I was still spotting and for some reason, I decided to take a pregnancy test and it came out positive. So I rushed to a clinic to get a confirmation and sure enough they confirmed it. Everyone told me to go to the ER because I was spotting. After being probed and poked, the Dr. informed me I was having a miscarriage. My question is, if I was having a miscarriage, wouldn't I have got a positive on the pregnancy test before I started bleeding? Could the Dr. be wrong? I am not trying to discredit the Dr. or even be optimistic about it, but if there is a possibility I can still be pregnant, I want to know. Also, I did not have cramps or blood clots throughout what I though was my period.