Needing help

thought it was implantation bleeding so i waited a week and took a hot it was negative. 3 days later i took another that was negative also. So I had given up even though I still had pregnancy symptoms. On the 27th I went to the Dr to get a test done and it was positive my hcg level was 62. The doctor told me I was having a miscarriage. 2 days later I took another test and it was also positive with a very dark line. I had an ultrasound done and the doctor said he didn't see any indications that I was pregnant on the ultrasound. I am so confused right now. Could someone please help