I had an ultra sound and showed a sac in uterus. Am I pregnant?

You may be if it is within up to six weeks after your last period. Before about five and a half weeks, the baby itself will not be visible yet; only the sac will be seen. Sometimes this can be a little later if the baby was conceived later than dates suggest.

Sometimes a baby may die very early on in pregnancy, or never develop at all. Then, only a sac will show. Then, the presence of a sac only indicates you were pregnant at some time but are no longer.