Vaginal discharge may be from several different causes such as bacterial vaginosis, yeast infections, vaginitis, or even retained tampons as you mentioned. More serious causes may be secondary to sexually transmitted diseases (i.e chlamydia, gonorrhea, trichomoniasis). Often times in women discharge may be the only symptom presenting. Given that you have experienced increasingly yellowish discharge over that past two weeks, I would recommend you make an appointment with your OB/GYN or Family Medicine physician