It looks like you are anaemic. If you have back pain
after you sit for long hours then it is due to your haemoglobin
levels as it is important to check that. Anaemia always leads to the symptoms of being tired and also having back / leg pain
though there may not be any pathological reasons for back pain
with your doctor.This is a general low back ache and for this you can follow these measures: one keep a pillow right under the knee while sleeping, next is you can keep ice in the painful area for about 5--10 minutes, if pain still persists you can stretch your body by twisting the waist on both sides how we used to do in the school drill similarly you can try which will help you relax as well will reduce the pain.