As you point out that it's on the spoke side of the tube, my guess would be that the rim tape is off. (Or worn.)
I had a similar problem, where I got a puncture roughly every week, and it turned out that the rim tape was moving. It looked OK when I opened everything up, but must have shifted when I put it together.
However, don't do what I did, which was to cover the rim tape with duct tape. While it did stop the streak of punctures, it also meant that the next time I had to take it apart there was gooey glue stuff everywhere.
EDIT
Change the rim tape. - Even if it looks OK it might shift when you pump the innertube.