Someone who has been through this or knows someone who has or even just someone who is educated in this kind of thing please help me..

So I went into the doctors 4 days ago, I was two days late for my period, I did I urine test which was a faint positive, then did a blood test which came back my hcg levels at 18, I did another blood test yesterday and today found my hcg levels are at 14, the doctor said that I've either miscarriaged or its an ectopic pregnacy. I had an ultra sound today because they wanted me in straight away, they couldn't see anything any where, not in my uterus, tubes or anywhere. I haven't bled , and I don't get bad pain, maybe just alittle slight cramping every once in awhile but that's it. I go back Monday to do another blood test to see where my hcg levels are. Does anyone know what could be going on? Anyone had this.. please help.