Am I pregnant?

I was just wondering if any one could help me out as I am going out of my mind, I had my last period the 22nd of August and I recently had unprotected sex 11 days ago, and i'm not due my next period until 19th September, only I think I may have been experiencing symptoms already, my ovulation date was the 2nd of september but for the last few days I have been experiencing nausea, and up until today I actually vomited 3 times this morning and felt very lethargic all day, I have been feeling dizzy, 2 days ago I had these really bad stomach cramps which lasted around 15/20 minutes, and I have also been experiencing slight lower back pain. I took a home pregnancy text tonight and it came up nevative. Do you think it is too early to tell?