Poor posture or Weights
I think you should recollect the posture or the actions while you had the initial pain. The other reason could be chronic ill posture at the computer which is commonly complained by people who work for long hours.
You should not carry weight for sometime esp laptop
You should lie flat on firm bed for minimum of 24 hours to XXXXXXX of 36 hours for the spastic back to be relieved
You should keep getting up from chair once every hour to relieve the pressure on back.
You can find images or videos on how to work infront of a computer and follow them.
There are certain exercises to be done while at work. Please do not work without proper working station.
Hope this helps.