Trying to conceive

Had sex on my most fertile days feb. 6 and 7th been taking pregnancy test I got one with a faint line the rest were digital test all said not pregnant. I've been throwing up and having lower back pain also stomach cramps my nipples are so tender and I feel bloated.. Also have short breath sometimes.. my temperature hasn't been below 98.00. My period is suppose to come on the 20.. I'm on cycle day 26....Has this happened to anyone? Any Suggestions Or Comments?