Shading periods in a scatter plot
 

I have a data entries that I'm plotting over time, and I would like to shade portions of it that correspond to different weeks. For example, Data entries 2 through five correspond to Week 1, and I would like for it to be shaded. I would just do it manually, but every time I add in a new data point, my shades go out of place because the graph is changing! Can anybody help me get it right?

Thank you,

Carlos Menegocci