Hi,
Usually free fluid in pelvis in ultrasound can be seen in conditions like during ovulation,
menstruation or in case of
pelvic infection. According to your description the possibilities are:
If you got the periods on around the expected date, then the free fluid may be due to the onset of menstruation.
The follicle could be ruptured
corpus luteum.
If you are not around the time of menstruation and got period before expected date, then:
If it is around the time of ovulation, the free fluid can be due to ovulation and the follicle could be maturing
ovarian follicle.
If you are having associated features like
vaginal discharge, pelvic pain, dysmenorrhea etc, then the possibility of pelvic infection should be suspected. And if you are having pelvic infection, there is possibility that your partner can also can get infected and vice versa.
So both of you should take the treatment simultaneously with your doctor's advice.
Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. Sree Gouri S. R., OBGYN