I get severe pain in my lower back when i've been doing every day activity like clean house or cook big meals and then lay down or sit with my feet up. the pain is a 9/10 and i cannot move my legs due to the severe pain. what could be causing this?

There are many causes to lower back pain, but when severe, it needs immediate evaluation (to both address the severity of it, and to rule out something which may need immediate medical attention). If the pain came on gradually over time without inciting trauma, it may be related to a degenerating structural change to the discs and/or the joints of the spine. There are many ways to address such.