I have found being in 52 week groups helpful in that they do get you taking photos that you wouldn't normally take, but if life is stressful, the last thing you want is more stress due to trying to find something to fit an arbitrary theme. One option is to join a group and do the themes that you have time for and just do your own thing in stressful weeks. I've also joined a group on Google+ which is just doing a theme per month. The whole challenge is to shoot B&W, so that will be quite interesting.