I have a knot in my lower back like a muscle knot. The pain goes down through my rear down to my legs. Is that what it is?
Not both legs just the left side

Since yesterday morning, my upper left back has been hurting me because I slept on it wrong. Yesterday, it felt like a muscle knot and it felt more relieved when rubbed. But today, it still hurts a lot but it feels like a pinched nerve. I don’t know which one it is, so I don’t know how to treat it. HELP!!! Any advice is accepted. Thanks in advance!