It could be a callosity due to prolonged positioning of the wrist on the computer table. This is just a probable diagnosis, given your history. The increase and decrease in the swelling could be due to bursitis which is a fluid filled sac which forms due to constant pressure in a particular part, in your case, the wrist.
Next Steps
Apply ice if it hurts, or else, it's nothing major to worry about. Try using a soft pad right under the wrist joint to prevent undue pressure over the callosity
Health Tips
An examination may be required for a better diagnosis