I felt my baby's kick around 15 before I use to just feel his body, since he would pop out lol and at 17 weeks hubby could feel his kicks outside. I'm a 2nd time mom, and at first you feel flutters, sometimes like lil lil gas, but its not gas. About the floating inside, it could very well be your baby, swimming in there, the sharp pain I don't,think is related if your baby was moving, it sounds like round ligament pain
The floating was more than likely the baby moving , if it was you will start to feel it more often :) its wonderful .
The pain was most likely something called round ligament pains and the floating feeling was probably your baby moving :)