A trace of free fluid in the Pouch of Douglas is very common and often normal, especially during ovulation. Because you have pain, the right medication depends entirely on the underlying cause. For mild, cycle-related discomfort, over-the-counter pain relievers like ibuprofen or paracetamol can help. However, if the fluid and pain are due to an infection, targeted antibiotics will be necessary. Since there is no single medication for this finding, please avoid self-medicating. I highly recommend consulting your healthcare provider or gynecologist for a proper evaluation to identify the exact cause of your pain and receive the correct, safe treatment.