Lady's who have been pregnant before

So I already have a confirmed pregnancy from hospital. I'm trying to figure out what's going on with me. As of now I'm playing the waiting games with my ob sooooo.... may 11 was my last period, I missed a period in June. But I really didn't think About pregnancy because my period is irregular . June 15 I went to the hospital because me and my friend caught a stomach virus they did a pt and it came back negative. On July 1 I spotted for 3 days took a test and got a negative on the 8th of July I got a positive a hour later I had got a heavy bleed just like a period with some light cramping went to my ob my hormone levels was 12.6 and nothin on the ultrasound. She said I could have be in a early pregnancy or end of a miscarriage. So when can you start to see a sac or what could be going on ??? Anyone with any good info