I'm not sure if i'm pregnant or not

My name is Meya and i'm 17 years old. I have a boyfriend and on the 22 of Feb. (I remember because I started my period the next day.) We were messing around alot. We've only had sex once that night.. and it was safe sex, but afterwards he was rubbing up against me and well... I heard that even if it just gets on your stomach it's still possible. But, i'm not on birth control. Never saw the use in it since I really don't like to sleep around, and i've only slept with two people in my entire life. But i'm a bit worried. I've been stressed alot lately and I find that I can't eat as much as i used to, like the sight of food makes me sick as soon as i take one or two bites. Then, i've been getting alot of headaches lately. I told my sister about it and she was joking around and asked me if I was pregnant. I don't really like to tell my family about my sex life in fear that they will disown me. What should I do... am I just stressed out and acting stupid about this? Or could it actually be possible?
And I can't really go to the store to buy a pregnancy test because i'm at home all the time watching my grandmother and even if I bought one now would it be too early for the test to tell?

Please help!