Thanks for the query.
An ovarian cyst
of around 5x3 cm size, with clear free fluid inside might be simple benign ovarian cyst generally.
Sometimes pelvic inflammatory disease
can lead to ovarian pathology. And because of that your doctor prescribed you antibiotic tablets
After completion of the course better to undergo ultrasound once again, if the cyst is still persisting better use contraceptive
pills for few cycles to decrease the size of the cyst with your doctor's advice.
And better to plan pregnancy after completion of treatment for the cyst.