You got pregnant a week after your miscarriage?
Ok, generally if you cramp but have no bleeding you should be fine, remember that the ligaments around your uterus are expanding quite rapidly now so aches are totally natural, I'm a little further along than you are but had cramping from around 10 weeks and it's nothing to worry about.
If you are very concerned see your doc and ask her to explain, they will understand your fears so don't be afraid to ask.
Best of luck