My Girlfriend Has Been On Prednisone And A Antibiotic And

My girlfriend has been on prednisone and a antibiotic and she has had brown discharge for 3-4 days and she has spotted 1 time. She has taken 2 pregnancy test and they all say negative. She even had a urine test done at the lab at the doctor and it came back negative. Would the steroids and antibiotic cause this brown discharge?