
Although it may not be wise to try and force yourself to write something it may be beneficial to offer yourself a small reward as an incentive. You don't need to complete it all at once, either - break your task into small chunks and then gradually piece it all together at a pace that suits you best. You don't need to do it in the right order, either. Sometimes I find it easier to begin writing a character's recent history first rather than their early years and vice-versa.