What Causes Abdomen Cramps And Constipation With Slight Brown Discharge?

my period is 12 days late, i did experience slight brown discharge around 14 days ago but which lasted a few days. i have occasional mild stomach cramps, i feel constipated, and very tired. swollen breasts, & sore nippples. i did a pregnancy test 1 day after my missed period it said negative. are these signs of early pregnancy.? i am 22 years old & have been trying to conceive for one year.