As per the ultrasound
findings and symptoms you have mentioned it suggest you have pelvic inflammatory disease
Repeated episodes suggest it might have occured from ascending genital infections. You should get proper genital swab and culture tests done this time also and start antibiotics accordingly. Also ask your husband to consult a venerologist to rule out STD's.Treatment of partner simultaneously is most important to prevent repeated attacks.
Since your ultrasound shows no changes of the fallopian tubes or obvious collection in POD, dont worry much.
I also advise you to use Condoms while your contact to avoid further episodes.
Also maintain personal hygiene.
Maintain adequate hydration.