Lower back pain 😖

Hey guys 🙂

So im currently 18 weeks + 3 days, for a while now ive had this really bad pain all the way down in my lower back by my tailbone but its only on the left side. It doesnt hurt unless im walking for a while or i move a certain way, but it doesnt go away. The pain will sometimes shoot down the back of my left leg and it can get pretty painful for a second and then it goes away when i adjust how im laying or standing. Has anyone else had anything like this? Ive had the pain for a long time but it seems to be getting worse. Im going to bring it up at my next doctors appointment but for now im jw if anyone has any idea what could be causing it and how serious it might be. 🤕