Post-ultrasound dread

My ultrasound yesterday was okay, but didn't provide me with the reassurance I'd hoped for. The good: there was a gestational sac and a yolk sac. (No one's ever mentioned me having a yolk sac before, so that's really positive!) The scary: I measured closer to five weeks rather than six. The doctor thought it looked good for around five weeks, and he didn't seem worried. It could make sense that I would be measure behind, since I ovulate a few days later than average. So intellectually I understand that everything might be progressing just fine, but emotionally I remain pretty freaked out that I didn't appear "on schedule." The doctor suggested that I come back in two weeks if I could wait that long. I said I couldn't wait, so I go back next Friday. In the meantime, my nausea is increasing - I had to leave the grocery store today because gross-looking food kept making me gag. I am grateful for every little sign.