It seems that you are not pregnant. It is almost impossible for a doctor doing an ultrasound
to check for pregnancy
and to miss it.
Your symptoms were either psychological or maybe just premenstrual symptoms.
You should take the medicines as advised by your doctor and keep regular follow up.
Also do not stress
too much and improve your diet with nutritious food and take up regular moderate exercise.This will help you better to conceive along with your medicines.