I went through something similar a few weeks ago with my putting. Couldn't hole the short "knee-knockers" that you just have to make to save my life. Basically I experimented on the practice green and found that I was tending to overread my putts and miss high. So definitely think about any tendencies you have as far as what side you're missing on. Also, I moved the ball back in my stance by about two golf balls. For some reason that kept my putts more on line and freed my stroke up. But you obviously have a solid stroke, being a 3 so just work on different things and you'll find it again.