There are many possibilities... my first advice would be STOP beating yourself up over it... (let someone else have that ~priveledge~
) You have been inside your body for HOW many years now ???? This trouble and those like it will NOT disappear over night. Adheasions, contractions, and physical tension... took a while to become that way. It will take time to reverse them. If reversing them was instantanious, it would be a pill
not a practice.
It is likely you have the same lower back & pelvis muscle tightness that most of us do. To get at some of those core muscles will take careful study on your part, and or by someone who is a trained & experienced yoga instructor perhaps? Simple stretching sequences, the Hatha-Yoga "Sun Saluation" might be a place to start....
My gut reaction is you require a LARGE bolster pillow to place under you when you do sit cross legged. Take the strain off the lower back, maybe reduce the pressure on your calves. www.YogaJournal.com
has some decent sections on how to do certain stretches, achieve certain physical positions and a large membership who could certainly help if better advice does not appear here. Hopefully keeping this active will get others to assist more directly.
Merely my opinion, I could surely be mistaken,