Because, as my chiropractor always says, motion is lotion…
The most you sit and it feels achey and heavy, the more that is going to happen. You gotta move!
I find a combo of movement (cardio) plus strength plus stretching helps. Not just leg exercises—whole body.
Start with some whole body movement in yoga like sun salutations. You can start to release the low back and open the hips with child’s pose too (which is part of Sun salutations, if you so choose)