FIG. 1 is a right side elevational view of a showerhead assembly showing my new design; FIG. 2 is a similar right side elevational view of the showerhead assembly, with a part of it shown in partial length for ease of illustration; FIG. 3 is a left side elevational view thereof; FIG. 4 is a front elevational view thereof; FIG. 5 is a rear elevational view thereof; FIG. 6 is a top plan view thereof; and, FIG. 7 is a bottom plan view thereof.