Welcome to HCM,
After going through your history and your description of Ultrasonography
,it looks that you have Ovarian torsion and if it settles down with conservative treatment it is all right.
Please discuss with your Gynecologist,about the possibility of recurrence as in such cases it is possible that it occurs again and if blood supply to Ovary is obstructed.
It can be fixed with surgical correction and it can be fixed so as to prevent recurrence by procedure called oophoropexy.
If damage is there to the blood supply and necrosis
is there then it may be necessary to remove that ovary.
Please take care