Do you cross your legs?
Do you tend to cross the same side all the time?
Is it uncomfortable to cross one side?
Do you sit knee over knee or ankle over knee?
People that always sit knee over knee when they cross their legs will often have a leg point up when they sit ankle over knee.
Try sitting both sides ankle over knee, one at a time. Do the legs lay flat or do the knees point up? If the knees point up, sitting this way will help increase flexibility in the hip and the leg should start laying flatter. As this starts getting easier you can start adding some resistance by pressing down on the knee. Don't force it hard putting pressure on the knee joint. Stretching more often is better than stretching it hard. Always compare left side to the right side and spend more time on the knee that is higher. You can increase the stretch by leaning forward, bringing your nose towards you shin. If the leg lays flat try hugging the knee to the opposite shoulder. Stretch the side you have more restrictions on to balance out both sides.
Many people with low back pain can feel better if they check for restriction and balance both sides out.
Sitting uncomfortable once in a while might do your body good.
There are other effective stretches you can do from a lying position.
Most people are stiff in the morning, so why not loosen up the back a few minutes before getting up out of bed.
Lying face up bend your knees with your feet flat on the bed. Gently, rock your knees side to side 30-60 seconds to loosen up.
Place your left ankle on top of your right knee. Use the weight of your left leg to pull your right leg bringing your knee towards the floor. Relax and let it stretch trying to keep your back to the floor. Repeat to the opposite side.
Place your left ankle on the right knee again but this time press your left knee away with your left hand and extended arm. Hold the stretch, then allow the left foot to lower to the foot on the right side while still on top of the right knee. Repeat to the opposite side.
Besides the stretching you can release tension in the gluteal muscles with a tennis ball. Lie on the carpet with bent knees feet on the floor. Let the knees drop to one side and place the tennis ball under the gluteal muscles on the other side. Bring the knees back to the other side over the ball. If it is too tender bring the knees back a little to take some pressed off. The areas you want to work are coming up and across the top to the outside of the gluteal muscles. You can hold still over the spot or rock the knees side to side. Bring the knees to the side away from the ball and reposition the ball to a different area. Spend more time on areas where you feel tenderness.
Most people feel a difference within two weeks. It took a while to get the restriction, so give it some time.
Just remember, "more movement less pain".