AM I REALLY PREGNANT

I was having right side backache on Tueday 18th of this month and on Wdnesday 19th the pain moves to the left side which I couldn't bear it any longer so my husband took me to the hospital that night because I couldn't sit nor sleep just crying. The pain get worst that it starts to affect my stomach bit by bit and the Doctor did a scan which he could not see anything. Then I went to pregnancy test where they take blood from me and the result came out positive but the doctor said how when they scan again and couldn't see anything. I also did my last menses on 27-31 of August and I am expecting my menstrual cycle today. Please am I really pregnant? I am feeling bad when the doctor said that it is not possible. Although I am still having turn by turn backache but not as much as b4