Slow rising hcg

I found out I was pregnant 14 days ago and since then it has been a whirlwind. My first hCG bloodtest done that day and read 1,238. I had another done two days later and it had only increased to 1,817.

My doctor was obviously concerned, and told me to wait four days, and then go back for another test. My third test was 3,785. I spoke with my doctor on the phone, and she said she is still concerned, but because I have no spotting or bleeding of any kind, no cramps, and I do have other normal pregnancy symptoms (mild nausea, sore breasts, etc.), she is "cautiously optimistic". Her concerns were a miscarriage or an ectopic pregnancy, but said she has seen slow rising hCG levels in normal pregnancies as well. I have an ultrasound tomorrow to see what's going on. 

Has anyone else had slow rising hCG levels that ended up being a normal, healthy pregnancy? I feel a little better after the "cautiously optimistic" comment, but this is my first pregnancy and I am still pretty concerned.