Well I'm not going to say "I'm sure it's fine." because I'm not. I will say that if you're still tired as heck, that's a good sign. Because you've had three miscarriages (I've had four, so I know how nervewracking this is) I'm sure the doctor would be fine with having you checked, maybe do bloodwork to make sure your HCG levels are still rising. Or even do an extra ultrasound?
My last pregnancy everything was right on track with a healthy heartbeat and a due date, then all of a sudden - literally overnight - I wasn't tired, I wasn't sick, I felt totally back to "myself." The baby's had died and I started bleeding at the end of the week and had a D&C.
Yes, things may be just fine but you'll probably spend the rest of this preganancy on pins and needles anyway, and that's normal and ok. Yes, things may not be fine and you may have to endure the heartbreak again of losing another baby. Over a year later and I'm still not really over it, and we've chosen not to try again because I can't even begin to imagine losing another.
I guess you can try to mentally prepare for the worst but hope for the best. That may not be the happiest, most positive advice, but it seems for some that it's the reality.