If it's starting to sound like a deasil engine it could be a hundred different things. Anything from a valve spring, lifter, oil return/feed/level issue or even a crank bearing. Start with the simple stuff.
Check your oil.
While you're at it get a cheap magnetic probe you can stick into the swingarm/oil tank. If you don't have metal shavings on your plug or in your oil tank than it shouldn't be anything too serious.
Good luck