As I've worked with thousands of homeschoolers, I've developed a checklist of reasons why homeschoolers may be lazy, lackadaisical, or unmotivated couch potatoes resistant to learning. Many times, motivation is affected by technology. You can read my article and find out more about how technology affects your home in, Balanced Technology in Home Education, an excerpt from my book Technologic: How to Set Logical Technology Boundaries and Stop the Zombie Apocolypse.
Look over this list, and see if you can further evaluate why your teen is causing you grief right now.
Remember that your goal is a general love of learning. You can't make them "love math" or "love writing" but you can help them to not hate it, so they can retain their general love of learning.
Need more help? I have a motivation section in my online resource High School Solution.
One of the two of my free classes, College Applications Simply Explained, had to be rescheduled last week because I was sick. So, if you missed the one I did