And if I take a pregnancy test and it comes back negative, is there still a chance I'm pregnant? (although I haven't done a pregnancy test yet, this has just happened to a friend of mine.)
For a while now I've been having unprotected sex with my partner. I haven't missed a period but I'm feeling really sick in the morning when I first get out of bed and very ill again about mid to late afternoon, the sickness is in the top part of my stomach(kind of bellow my ribs to the top of my belly button.) it isn't painfull, just completely nausiating. I haven't thrown up or anything but I'm feeling sick a lot of the time. Has this happened to anybody else? And what are the chances this could be a pregnancy in its early stages?

You're having sex, so yes, you could be pregnant. The fact that you're having unprotected sex just increases the odds.

No one can tell you if your symptoms indicate pregnancy. Some women will have your symptoms and be pregnant, others will have your symptoms and not be pregnant. Every woman is different and every pregnancy is different.

I'm afraid that the only way to know for sure is to take a pregnancy test. Use first morning urine as it's more accurate.

Also, yes, a negative pregnancy test can still mean your pregnant. It could be that the test was taken too early, the hcg levels weren't high enough, the test was faulty. If your friend still hasn't gotten her period 1 or 2 weeks after testing, she should re-test or see her doctor.

Good luck.