Any idea what could be causing lower back pain when I lie down? Sharp, lasts for a few minutes and then goes away.

I'm 20 and I've noticed this for a while, at least a couple years. It hasn't really gotten any worse. I'm normally fine, but when I lie down flat there's a diffuse sharp pain in the small of my back that lasts for a few minutes and then fades away to nothing. Doesn't happen when I lie on my front or my side. Especially noticeable after I've just done some kind of physical exertion, like right now for example I lifted a heavy mattress upstairs and lay on it and it triggered the pain.

I was on Accutane (isotretinoin) a few years ago for acne and this started around the same time, I know it can cause joint issues so could it maybe be related? Not a big deal just would be interested to know.

Cheers!