Low, Slow rising HCG, but fetal heartbeat found

hello all! Let me start by saying to congrats to all the expecting mommies out there, I'm so happy for all of you! I am also 7 weeks prego (per LMP), but believe I am close to 5 weeks (per ovulation calendar and reg periods) I'm pretty sure I conceived on 4/28 . I went to the ER due to some spotting and cramping and had my HCGs checked and they were very low. I then had them repeated ever 2 days and they went up normally as follows:

5/13 = 51
5/15 = 122
5/17 = 307
5/19 = 593

Low, but looking good, right? so then no more blood draws for a while...then more cramping and pinching on right side of pelvic area. SO to rule out ectopic, my Dr ordered  more betas, but this set is not so promising:

5/26 = 2424
5/29 = 2647

My Dr was not happy with these results and told me to prepare for termination. She scheduled an U/S to find the pregnancy location so we would know the best way to terminate, and there they found my little bean, heart pumping @ 125 BPM. The Dr says this is slower than she expected and has scheduled me to come back in a week for another U/S and one more beta, which was:

6/4 = 3332

still not doubling. These numbers are KILLING me. I guess I'm so nervous because I just had a miscarriage (blighted ovum) in feb and my fiance and I very much want this baby. Any similar stories out there with happy ending?