Can someone help?

This is my February Cycle.... Now Glow told me I was ovulating on the Monday/Tuesday. But my CM was talking a different story. It was quite watery anf creamy... And then on Thursday is when I experienced EWCM for two days. Now I went to bed with a mild headache.... And woke this morning being quite sick... And feeling nauseous.... I took a pregnancy test two days ago and it was a definite negative. I'm just wondering if I could still be pregnant but the pregnancy test I've been using haven't picked anything up? They are cheap ones from amazon?