Scared

So I went in for another Dr appointment today, and I figured they would do the heartbeat and maybe run a few tests. I thought they were going to do a fetal heart tones but ended up with an ultrasound. I had a different nurse as well (one I liked though, which was good). She ended up not being able to find the heartbeat, and was getting confused if she could even find my uterus or not, she couldn't tell if it was my uterus or my bladder. I had just read that it can be kind of hard to tell sometimes in early pregnancy between the two, and that a full bladder helps them see to the uterus. The nurse spent like 15 minutes with a puzzled look on her face, and then said she couldn't really see, and she would go get the Dr to try and see if he could get a better picture.
Short wait later, and he came in. Round two of ultrasound. At this point I'm a little nervous about everything. He asked me what pregnancy this was for me, which is 2. He asked if I already had a child, and I said I had a miscarriage. He asked what week I was supposed to be, which is 11, and told him that I got a positive pregnancy with ultrasound at 6 1/2 weeks on February 22nd. He then asked if I had a D/C with my miscarriage, and I explained that the ultrasound tech said that everything happened naturally and I didn't need one. He said something about a two (He's middle eastern, and kind of hard to understand fully, I think I need to find a new OB), and then said he was concerned, and that I needed to schedule another ultrasound with the actual good tech named Sally tomorrow morning. He said I may have to go on hormones, and something about infertility doctors, but we'll wait until tomorrow and see what the ultrasound tech Sally says tomorrow.
So the appointment is for 8:45 am tomorrow, and I'm scared to death. 
We made the appointment, and 30 seconds after walking out of the clinic, I burst into tears. Ken and I sat down near the elevators and he held me while I cried. I told him how I didn't understand, we had the positive both with a pregnancy test at home and with the ultrasound, I've had no bleeding, what was going on? He told me to try not to stress, that it may be nothing to worry about. I cried basically the whole way home, and Ken sat with me again on the couch while I continued to cry. Nothing makes any sense, and I don't want to go through the emotional turmoil of losing this baby. It was hard enough last time with the miscarriage, I don't know if I can handle something else being wrong for the second time. I shared with Ken about my fears, that my emotional strength wasn't enough if something was wrong, that all I want is to be a mommy, and I'm scared to death that I won't be able to experience pregnancy and having kids. That something is wrong with me and my fertility.
I just don't understand?! How can things be great at 6 1/2 weeks, and magically go so wrong at 11, with no bleeding, no pain, nothing to explain it? It's been such a draining day, and I'm trying not to be pessimistic, but it's difficult when there is a possibility you may not be pregnant like you thought. Lord, please give me the strength to make it through this.