Pregnancy or stress ?

Hey, me and my gf have had a few bouts of un-protected sex as early as a week ago, but in none of the cases did I ever go in her (which I know isn't 100%). After Thanksgiving she felt sick in the stomach, but of course I believe it was just over-eating. The next day she said she dry-heaved and felt sick in the stomach. She has felt a little tummy ache/discomfort ever since. Along with that, she said her urine was "cloudy" on one occasion. She is also a few days late on her period (she usually gets its 26-28 days, and it is roughly day 31). We decided to try a pregnancy test this morning, and the first one came up negative. She thought she didn't do it right, so we went out and tried another one... also negative. Tonight she said she had gone to the bathroom and seen thick pink mucous I guess from her vagina....and that she had never seen before. Other than those above, no other real symptoms have occured. I know she has been real stressed over the last few months to possibly be the reason for a delayed period... any thoughts on this?