After Having My Monthly Period I Started Having Brown Spotting,

after having my monthly period i started having brown spotting, sometimes pink, and sometimes with the blood..it's been 2 weeks now and when the doctor had tested my urine, my urinalysis are normal and no infection is found..my blood test is also fine and i am not pregnant...today i started having sore nipples..can anybody inform me on what is going on in my body..