Lower Back Pain

Hi, been having lower back pain. Its all good when i lift, during training. The problem arises on the rest days or atleast i feel most discomfort then. The pain is not severe but its annoying because its always there. Then i start to train and all is good. What the hell is happening? Could it be that my core is weak? Things i have tried. Got a trapbar, started doing foam rols, started stretching, started reverse hypers. Thing it helped some but i want to be pain free! Help!

Thanks for the reply. Never crossed my mind im just cold. Gonna start implementing all your suggestions. Have a good one!

Sorry, I dont know how my post got deleted, maybe a moderator can fix it.