Loss of symptoms at 8 weeks?

Ive been horribly fatigued and nauseous since week 5 - and a bit constipated - and on Saturday all those symptoms disappeared. I'm currently 8 weeks and 3 days . On Friday I had an ultrasound and saw a strong fast heartbeat, but losing all my symptoms the very next day has me freaked out. Called the dr and they said not to worry unless I'm
​Bleeding and cramping - but I can't help but worry. Anyone else lose symptoms suddenly this early??