What Causes Fluid In The Uterus?

i went to have a hycosy scan, and the doctor performed a transvaginal ultrasound first. the doctor said she was not going to prceede as the scan showed fluid around or in uters (can not remeber which one) the doctor said i had an infection and that i would need antibiotics, but sent me home from the hospital without any but told me to wait for a letter!!!! and i am left wondering what this infection could be and could it be causing damage to my reproductive organs?