Alternate y-axis in Plotting

I am using Plots to build a plot line by line. My initial intent was to plot one line using the left y-axis and then the next line using the right y-axis. For the first time through, using twinx() works well. However then I cannot seem to figure out how to plot the third line on the left y-axis. Using help on twinx() seems to indicate that this is not possible. Is there another command that will allow me to control whether to plot a line on the left or right y-axis?

One try is given below.

julia> x_arr = sort(rand(10));

julia> y1_arr = x_arr;

julia> y2_arr = 1.1 .* x_arr;

julia> y3_arr = 1.2 .* x_arr;

julia> y4_arr = 1.3 .* x_arr;

julia> ep1 = plot(title="A Plot", legend=:topright)

julia> sep1 = twinx(ep1);

julia> ep1 = plot!(ep1, x_arr, y1_arr)

julia> sep1 = plot!(sep1, x_arr, y2_arr)

julia> ep1 = plot!(ep1, x_arr, y3_arr)

julia> sep1 = plot!(sep1, x_arr, y4_arr)