Lower Back Hurts When Lying Down

I’ve noticed this problem for a while now. Whenever I lie down flat, either on a bed or on the ground, my entire back hurts like crazy. However, when I arch my back while lying down, the pain goes away. I have noticed that I may have a slight anterior tilt and was wondering if this may be the cause of the problem. Nothing hurts when I’m standing up, only when I’m lying down. I don’t have any back pain after doing back exercises, and I haven’t trained rigorously for about a week now (I decided to take 2 weeks off). I was wondering if any of you have had this problem, and if it’s due to muscle imbalances, tight muscles, or anything else. I’ll try foam rolling to see if it helps but I’m not sure. Any one have any ideas? Thanks a lot.

Man, this could be a ridiculous number of things.
If you can, take a picture of yourself relaxed, side view and post it so I can get a better idea of the extent of the tilt.

Does one side hurt more than the other?

I find this happens to me especially if I do adductor stretches and then lay down. It’s probably a tight psoas. Are your traps generally tight? Are you often stressed?