If it is prior, then you do need to use plotyy as you have done. The issue is, there are actually 2 axes being created and the Current Axes is the one on the left. So, you need to get both axes back which means navigating the graphics hierarchy.
f = gcf; % Get Current Figure;
ax = f.Children; % Get the axes array
rightLabel = ax(1).YTickLabel % Here is the Label you were looking for
Replace any of the above with get and set methods if you wish:
f = gcf;
ax = get(f,'Children');
rightLabel = get(ax(1),'YTickLabel');
