Different scans will show different things. It depends on a lot of factors. With DS I saw a heartbeat at 5+6. With my second pregnancy (ended in MC) I had a scan at 6+4 (was actually 5+6) and saw a sac with fetal pole but no heartbeat.
Can you give us a bit more info? Are you 5+0? If so I would say don't worry unless you've had other symptoms such as spotting or cramping which might be a cause for concern. If not, then the chances are all is fine but it's just too early to spot anything yet.
Did you have an internal scan? Often external ones at this stage show up very little.