Sad news. (Long post)

I found out I was pregnant on the 6th of sept I started bleeding on the 11th and miscarried on the 13th. After that I wasn't using any concraception I was getting sore boobs & having had a period I instantly thought I was pregnant again, I took a pregnancy test on the 28th & it said not pregnant (I know having a miscarriage, in your body the HCG levels are still in your body and can still come up as pregnant) but I did take a pregnancy test, and it did say NEGATIVE. & so I thought that was the end of it, I still didn't have a period so I took a pregnancy test on the 15th of October there was too lines which was very faint and I took a clear blue which said pregnant 1-2 weeks.  I didn't know when my last period was so my doctor put me forward for an early scan, my doctor was doing an ultra sound @ there was nothing there? & she done an internal scan, still nothing.. I still haven't had a period & boobs still hurt I'm so confused, she was saying maybe because I had a miscarriage I still had some hormone still left inside my body but on the 28th it said I wasn't pregnant? I'm instantly concerned my doctor also asked me to do a pregnancy test and I t came up negative? I'm very concerned & worried? The ultra sound lady didn't seem concerned at all? I'm just so confused!😔