I am like that often as well. I work full time and I get wore out.... even though I would prefer to be at my sewing machine I need some real motivation. I don't have the answer. Sometimes I just "push" myself - - much like I would push myself at work when the boss tells me to do something
usually once I get over the hump of starting I am glad that I got started. I also found having a few different projects helps me. If they are all at different stages I can usually find one at a stage that I can get in the mood for fairly easy