One thing might be you pushing yourself too hard. Take breaks and rests. It may sounds like wasting time, but you will feel refresh after that. Since you are only able to work on your project at personal time, I suggest to push it to early morning, before you go to work, where it has no interruption, probably will increase your productivity. After you back from work you already exhausted, which might not be a good time to work on something else, considering you have spent most of the brain power at your work.
Set a small and achievable goal for each day. Most importantly, rest in between.
Good luck