Why can't my radiator heat up my bedroom?
That radiator certainly looks big enough to heat the room you describe. 

The windows -- Maybe the living room window is better insulated than the bedroom window. You may be able to feel the difference by resting your hand on the glass. Also, the living room drapes may be better insulators than the bedroom curtains. 

Drafts -- You can use a joss stick or a punk stick to detect drafts, and to monitor the convection in both rooms. You will have to sit still for a minute to let the eddy currents from your moving around to die down. 

With concrete construction, any cold drafts would likely come in around the ceiling, or around the window. Also check switch and outlet plates. 

Convection -- When a radiator is under a window, the downdraft from the window fights with the updraft from the radiator. Usually one or the other wins out, so there is circulation throughout the room. Maybe in your case they almost balance. 

The real mystery is, of course, why the convection in the living room is so different from that in the bedroom. With patience and joss stick smoke you may be able to see what is really happening. 

A remedy -- In my house I had a similar problem. I solved it by adding a room fan, on its lowest setting, to move air over the radiator. My bedroom went from uninhabitable to toasty. If you have any kind of fan or blower on hand, try experimenting with blowing against the wall below the radiator to assist the natural convection. 

If this works I would suggest two small (5 inch or 8 inch dia) table rotary fans placed on the floor, about 4 inches from the baseboard, blowing toward the radiator. I would rewire the fans in series for lower speed, but that's just me.