Miscarriag/Ectopic/or New pregnancy?

On Nov 28 I began spotting lightly (pinkish). Then, on the 29th I got what I thought was a normal period. It was on time and everything. My periods usually only last 4 days, maximum 6. When the bleeding had not stopped by day 13 I went to the Dr. to find out what was going on and was promptly sent to the ER. While in the ER I was given a urine pregnancy test that came back positive. The blood test showed my HcG level to be about 100. (This was around 6pm) The ultrasound however showed an empty uterus so the Dr told me I was having a miscarriage. On day 16 I started having horrible upper abdominal cramps which I believed to be unrelated and went back to the ER. I went to a different one this time. When they gave me a follow up blood test it showed my HcG level had risen to 180 (this was around 11am), but the ultrasound still showed nothing. They checked my fallopian tubes and ovaries as well and did not find anything. After many, many hours in the ER I was transported to another facility to see an OBGYN. The conclusion was that I either had miscarried and they didn't know why my levels rose, was having an ectopic pregnancy that they could not find yet, or I am just in the early stages of pregnancy and it is too early to detect anything through the ultrasound. They said my levels had not quite doubled so it was hard to say if I am in fact still pregnant at this time. They said the stomach pain was gastritis due to the pregnancy, whether I still am or not. On day 13 I was only spotting lightly (brown) when my urine and blood tests came back positive. On day 16 I had stopped bleeding and my HcG level had gone up. I am going for more follow up blood work tomorrow, but it is bothering me that they could not explain anything to me. I am extremely stressed out right now and it will take a while to get the results of my blood work back to get any answers. I had no cramping except the first day or so of what I thought was my period, and it was NOT extreme. I miscarried this past January and the bleeding only lasted 7 days, but the pain was excruciating and I was put on bed rest. This was nothing like that. My HcG also returned to zero fairly quickly the last time too. I still FEEL pregnant, but have read that I might for a while after a miscarriage. Is it possible I really could still be pregnant, or is the rise too low to tell? Is it normal at all for HcG levels to rise at the end of and after the bleeding has stopped after a miscarriage? And, if it is ectopic, wouldn't they have found something? I feel like they don't REALLY believe it is that, or they would not have discharged me.