Gestational sac only

Hi all according to my LMP, I am exactly 7 weeks today and I got my 1st vaginal scan. However, there was only a 7mm gestational sac and ultrasound says its 5w4d. I've only had bloating and felt extreme fatigue with a little cramps once in awhile. No nausea/vomiting. Dr asked me to return for a rescan in 1 to 2weeks time. I'm very worried now cos mine is a 28day cycle mostly. Any advice? Do I go back for a scan in 1 week time or should I wait for 2 weeks?#pleasehelp #firsttimemom #advicepls