Miscarriage question

I found out I was pregnant march 1st with a hpt I went to the doctor on the 2nd and had another BFP they expected my delivery date as oct 26th I started spotting on the 3rd and got very nervous I went in and my HCG were only at 37 and I got a BFN The doctor said I had probably already miscarried. In my ultra sound they also didn't see a baby? Then on the fourth my flow became really heavy. Was this a chemical pregnancy or what? Sooo confused!! Please help!!