Hungry Joe

I had been riding around on my DIY fixed wheel (I know, I know, but I was broke) and then it seemed to me that I had stripped the hub, so when I had saved up some cash I bought an IRO wheel, a Soma cog, and a lockring from Tony. Because I didn't have a chainwhip or a lockring wrench handy, I tightened the cog using the Italian Chaingang method (it's been linked to on this forum) and just tightened the lockring by hand - I rode this for maybe two miles or so before getting to the LBS so I could tighten it all up proper. That all went fine and then I rode it home and then later that night to a friend's house. On the way back, I tried to do a skid and the cog spun backwards enough to startle me. A minute or two later, it spun forward about the same amount. The next morning, I checked the lockring and it was a bit loose so I tightened it up. This morning, though, the same thing happened when I was applying some backward resistance while coming to a light at the bottom of a hill. However, it's not spinning like a freewheel, just spinning some of the time.

So my question for all of you is this: Is it possible that through some tom-foolery, I stripped my hub already? Or could it be a loose lockring? Or maybe even a chain skipping (I've had the chain since late February - it's a 1/8" chain, as the cog on the DIY wheel was that size)? Any and all ideas, mockery, and (un)constructive criticism is welcome and appreciated, as long as it's not about the old DIY wheel.