I also don't know what's going on with his sleeping habits. Within the past two months, he will not get up no matter what I do. He will sleep until 12:00, 1:00, or 2:00 in the afternoon. Maybe he is having a growth spurt?
If it's any comfort to you, recent studies suggest that as kids enter their teen years, their bodies require a lot more sleep than previously believed. One study indicated that their sleep requirements resemble that of a toddler. However, in my opinion, routinely sleeping until 1:00 or 2:00 in the afternoon is not acceptable.
It sounds like you and your son need to sit down and have a serious discussion about your homeschooling future. Pick a time and place where there will be no distractions and you are both calm and relaxed. Ask him what he hopes to accomplish the next year, what he sees himself doing in the future, and what he likes and dislikes about the current homeschooling arrangement. Be a good listener try to see things from his point of view.
Next, discuss your concerns and explain why certain issues are troubling you. Then negotiate a contract with your son, compromising on certain issues and setting boundaries for others. For instance, you understand his need for sleep, but now the rule is he must be up by 10:00 a.m. or he will forfeit his Nintendo privileges for that day. Don't be afraid to follow through a 13-year-old needs firm but loving guidance. On the other hand, if his work assignments are troubling for him, find another program or create your own. I have never followed a curriculum or given my daughters "assignments." For creative kids, following a full curriculum is just too boring. This may be what's happening with your son. For helpful ideas on how to jump-start the learning process, read Motivating Your Homeschooled Child.
To help you set up a comprehensive program you both can live with, I suggest you read Homeschooling: The Teen Years by Cafi Cohen. As a single parent, homeschooling a teen can be very difficult. Try to connect with other parents of teens by contacting a local homeschool support or resource group. And lastly, don't be discouraged. As your son matures he should become a bit more cooperative and reasonable. Good luck!