You seem very young. And I hope that you will use protection the next time you decide to have sex. It only takes ONE time and ONE sperm to get pregnant. The only way to know is to see if you are late and take a HPT. As for the empty feeling. Maybe it is just nerves from worrying over the possibilities. I hope you are okay. And please be safer next time.
--J
Some people disagree, but I don't believe you can "feel" pregnancy the day after unprotected sex. The egg needs to be fertilized, then make it down to the wall of your uterus and implant (this takes about 6 to 12 days) before your body knows you are pregnant and starts producing the necessary hormones to support pregnancy.
sounds to me like you worked up an appetite.
you would not have pregnancy symptoms this soon after sex. if anything, you would most likely be experiencing nausea/morning sickness(if you were somehow pregnant)but its even too early for that.
You wouldnt feel any sign of pregnancy that early after unprotected sex, Only way to tell is do a hpt then we will all know!