What other reason could there be for l spotting other than pregnancy?

ive been spotting since just after ovulation,,im due my period around monday,,,ive been spotting a tiny amount of pink/light brown about 2/3 times a day ,,also had cramping,,,im relay hoping im pregnant as we've been trying for 3.5 years,,,all pregnancy tests so far are negative (1st response) and ive recently has a smear,,all clear, (had smear after spotting started),,also had a recent menopause test,,all fine,,im not sore, it doesn't smell offencive, im not itchy and it doesn't burn when i pee,,,,