My last cycle was Oct 1-5. On Oct 26th I had some redish pink spotting and I thought AF came early (it was due for Oct 31) so I changed underwear, put on a pad, and several hours later there was no blood/spotting/anything. I tested Oct 29 because I was feeling nauseas and a little light headed. It was negative. I ended up in the ER the next night (Oct 30) because of pain in my left side and shortness of breath. They drew blood and took a urine sample and didn't mention/ask about me being pregnant then. I'm 20 years old, in average health (other than being overweight), not on any form of birth control (including condoms), and have never missed a period. Could I be pregnant and just testing negative or is AF just late?

Edit: Thought I should add that I've gained 6.5lbs and have been more emotionally sensitive. Also at the ER the dr told me my chest wall was inflamed and that was what was causing my pain and breathing problems.