ultrasound showed no baby #update

On Saturday to my surprise and total shock i took a pregnancy test and it came back positive! ive taken 3 hpts and two from the hospital urine and blood test, im kinda unsure of when was the last date of my cycle i had two periods in March, so yesterday i started to have this pain in my right pelvic area they did an ultrasound and later told me my results both my urine and blood test confirmed i am pregnant but the doctor told me they didnt see anything on my ultrasound my heart dropped but he also said it could just be im too early and to not worry wait a few days and recheck my hcg levels to see if its increasing , any other ladies had this happen

Update : first off I want to say thank you to each and everyone of you who took the time out of your day to answer my question and help to calm my nerves I just had a telephone appointment with one of the doctors and she did mention they didnt see anything in my uterus but my hcg hormone level was 1100 and since i got a negative pregnancy test on 4/6 and a positive on 4/14 and its unsure when i ovulated its most likely im very early in the pregnancy and they wouldnt expect to see anything on the ultra sound, she did order another hcg blood test to check to make sure my levels are going up, I will check back in once I have the results!