I appreciate your query.
Actually there could be one of the following possibilities
1. You have not mentioned normal cycle length. If you are overdue with your periods, then you could have had an early pregnancy
, which already miscarried ( since you have history of 4 prior miscarriages ) - the corpus luteum
( structure in ovary which supports the pregnancy ) could have ruptured .
2. Ectopic pregnancy - pregnancy outside the uterus - in tubes or ovaries, presents with this picture. Sometimes, pseudo sac is seen in this condition.
3. Rarely, heterotopic pregnancy ( pregnancy both inside the uterus and another sac outside )
The only way to differentiate all these conditions is by an expert, complete ultrasound
, detailed examination, blood pregnancy ( HCG ) tests and as a last resort, diagnostic laparoscopy
, if the fluid is significant from the ruptured cyst.
If your pregnancy tests are negative, as you mentioned, then other possibilities are - simple cyst
of ovary which ruptured, endometriotic cyst which ruptured or any other adnexal structure seen ( ruptured par ovarian cyst
PLease go for expert opinion at the earliest to diagnose your condition. Repeat the ultrasound and blood tests. Fluid from ruptured cyst cannot present as a sac inside the uterus