To save a jpg with saveas() you have to give a proper figure handle (at least gcf) as first argument and change '.jpg' to 'jpeg' as format specifier (no dot and including the "e").
clearvars, close all
NAME = 'myFig';
fig = figure('Name', NAME);
saveas(fig, sprintf('%s - F vs V', NAME),'jpeg')
However, i would recommend to use a vector graphics format or png instead of jpeg, because jpeg could contain ugly artifacts.