Very likely to be muscle and ligament sprain of the lower abdominal musculature. Any pain related to postures have more of muscular predisposition. A physical examination can conform this by various maneuvers of lower abdominal and upper thigh muscles (which have common attachment on the pelvis) and palpation of these structures will give fair idea. Physical therapy is the mainstay of the treatment with anti-inflammatory analgesics and cold compresses.
Please feel free for your follow up questions.
The ovarian cyst, if you meant by that, do not pain with the changing posture. The pain is usually constant. The ovarian cysts are most of the time asymptomatic. They become painful only because of the complications like sudden hemorrhage in them, torsion, twist or sudden increase in size. There is another condition called as Mittelschmerz, which is the pelvic and lower abdominal pain that some women experience during ovulation.
Your further queries are welcome.