your baby this early basicly shows up as a tiny blob in the sack, most times you cant tell cuz your baby is not formed enough. drs normally dont do a us till 7-9 weeks. and remember ultrasounds are not 100% you could be a few weeks off and they could get the sex wrong [it happens a lot] if youre wanting to know the sex, wait till after 21 weeks, its more correct that way [tho not 100%] good luck