I had this back ache for a few days, i'm pretty sure I did not strain it because I did not do any badminton recently or any other sports. The ache / pain just came suddenly and it's not to the point I can't walk or would affect my daily routines. Sometimes the pain is non existent, sometimes it is, during the night when i'm about to sleep or when I sit on the sofa, I do feel the pain much more, but when I lay flat on my back, I pretty much don't feel it. Just want some advice when is it a course of concern for me to see the doc ?