You should start taking prenatal vitamins now. Sometimes when they do an ultrasound early they see a sac but no baby, I guess the baby is not big enough or developed enough to see yet. I think the chances are pretty high you are still pregnant. Good luck!
Yes, you are still pregnant. It just means the fetus is to small to see on the ultrasound. From the dates you shared you are only 2-3 weeks pregnant. Alot of the times you wont see the fetus on the ultra sound or hear the heart beat until after 6+ weeks. Start taking your prenatals right away.
You should start taking prenatal vitamins immediately. You should have already been taking them. As far as the ultrasound goes, it could be to early to see much of anything other than the sac right now. You should be able to see something around 6-7 weeks of gestation, but it will still be small.