Dan,
I don't think laying on the side and being belly up will guarantee your female is gravid. My female hasn't been observed in strange positions since Jan and actually is much larger than she was the last time. She does stay in the warmest places and hasn't eaten since Dec 31. I have stopped offering food because I think she is gravid. Last time I kept thinking she was...then not the entire time.
Pretty exciting...and kind of nerve wracking trying to do everything perfectly.
Best of luck to you,
Linda
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"There is a principle which is a bar against all information, which is proof against all arguments and which cannot fail to keep a man in everlasting ignorance- that principle is contempt prior to investigation." Herbert Spencer