Period Earlier Then Usual , Have Some Pregnancy Symptoms . .

well , i had unprotected sex with my boyfriend about a week and a half after my period , and i was in that position where supposedly you can't get pregnant because of "gravity" . then the morning after i had headaches and i felt like throwing up , but for the rest of that week i didn't feel too bad and ate a whole lot . then about a week after that i started feeling a bit dizzy , fatigued , i always need to use the bathroom , started to lose my appetite , and then all of a sudden i got my period and it wasn't supposed to come until about a week later and my cramps were a bit worse than usual . i heard that you can still get your period while your pregnant .

is it really possible though ? can i be pregnant ? or am is it just all in my head ?