It is possible that you could be pregnant again. After you lose a baby, you are normally pretty fertile during the period of time afterwards. Did you have a d&c???If you didn't, then it's also possible that your body is trying to pass the remaining pregnancy tissues. If you had a sharp pain and are concerned, ask your doctor to perform an ultrasound so you know exactly what you're dealing with. If you find that you are pregnant again, please take your prenatal vitamins, go for regular check ups, and take it easy!
Goodluck!