Aching back

Sitting in front of the computer for a couple hours , I have got an ache in my upper back. It will be transient discomfort but it is not the first time that happens to me. No matter how I stretch my back muscles, it just can't take the edge off. Only when I completely leave my computer with my homework or chatting done did my ache lessen. It is endurable so far, but I need to finish my homework on the computer as soon as I can and that will do me good to have a rest for my eyes too.