What's the cause of my back pain?

For a few weeks now I've had a problem with the lower left portion of my back. I also get this tingling feeling in my upper left thigh too. I don't know for sure if it's connected, but it seems like it sometimes. The pain I get in my back happens mostly when I am laying down. So sleeping can be difficult sometimes.The thigh tingling is strange to me. I get it with the back pain while lying down, but I can get it without the back pain sometimes too. And likewise with the back pain, it doesn't always come with the thigh tingling. This tingling that I'm talking about occurs in my upper thigh and can almost feel like burning sometimes as well. I can't figure out the cause of this at all. I use to have a job where I did a lot of lifting, but I didn't get this problem till months and months after I quit that job. I haven't had any recent injuries that I can really think of either.