Look for the nuptial pad on there front feet. OK, say you are looking at the back of your hand. There should be a dark long bump between their thumb and wrist. It is not on the bottom of their foot, but more on the side there. it will stand out well because of their white feet and legs. They should have them if they are males by now considering that they are 3" long. Google pacman nuptial pads and look at some pics. If there are none on your frogs thumbs, then I would keep checking for nuptial development a few months and listening for a croak after the lights are off for 30 minutes or so at night. If they get over 4" long and continue to grow , you got females.