If it’s recently happened/have you moved something heavy, it might just be a pulled muscle, very painful & sore for a few days, I pulled my back out moving a generator when I was your age & I couldn’t even put my D Series Ford into 2nd or 4th gears, could only push the gear leaver forwards [emoji57]
If it’s muscle pain, it should clear up in a few days, a hot bath & or a hot water bottle on the area might help or ice to numb it for a few minutes, but still get it checked it out.
Your a bit young to have a Prolapsed Disc (or slipped disc) mine went’ when I was 40+, couldn’t walk for a week [emoji22], but you learn to manage the pain.
(& STOP JUMPING OFF LORRY BEDS !!! [emoji57])