if you are having to keep pointing downwind to stay on the plane, then sounds like you were a bit underpowered. its pretty tough to make ground upwind if you are sailing underpowered. maybe you need to rig a little bigger?
other then that, try reading this
www.guycribb.com/userfiles/documents/cranking%20upwind.pdfand if the wind is light and gusty, like it is most of the time here, what I do is slog upwind in the lulls until the wind comes through, helps make up a little ground. plus i can slog upwind pretty much as fast as i can sail upwind fulling planing lol