you could try a specific lumbar stretch: lie on the floor (get there any which way you can! ) and with knees bent tighten you abdominal muscles and focus on trying to eliminate the space between the natural lumbar curve and the floor by pushing down. i have the same problem at times and it helps.
when i first lie down my lower back erupts in sharp pain. sometimes it goes away sometimes not. i'm a 20 y/o female. lying on side or stomach is the same- laying down i have to tense up those muscles or its painful. if i arch my back the pain goes almost completely away and after a while i can relax without issue unless i'm lying on my front. i exercise every day; i have a desk job and i'm on my feet a lot. i eat right and don't smoke/drink. what do you guys think? i have tried stretching before lying down but i'm not really sure. how. i should etc. so any tips would be most helpful.