6 weeks is good. If too early (say 4 or 5 weeks), Dr might not be able to see the heart beat. Some Doctors will not see patients until patients are at least 7 weeks preg.
I guess 6 weeks is better. You should be able to see sac and maybe heart beat then. I went in too early, dr can't see anything yet in which makes me worry now. It might be worrying for no reason =P