Am I pregnant or just stressing?

Okay, so on and off I've missed taking birth control pills, and at the beginning of this pack, I was supposed to start the new pack on a sunday, but couldn't start until thursday due to a money shortage, and thursday being when I got paid. My boyfriend and I had sex before I started my new pack last wednesday, and since then due to the hours I work and sleep, I get distracted or forget to take my pill one or two nights, then when I remember the next day I'll take two. I've had sex a few times since last wednesday. I took a pregnancy test, and I figured it would come back negative, which it did since it's too early to tell yet. But the last three or four days my nipples have been a lot more sensitive than they usually are. I've been getting headaches every once and a while. Sometimes I munch all day, sometimes I feel like if I eat, I'm gonna throw up. I've been really tired, but I figure thats due to working. I don't know what to think, any help from someone with experience would be wonderful. I'm 20, but this is my first questionable experience in this area.