Generally the older the frog, the less frequent they poop. It is possible that your frog had already pooped but it escaped your notice? If you are using EcoEarth there may be a poop in it. But if you've been keep the frog on paper towel then never mind what I just said.
Personally, I would not stop feeding just because of the frog isn't pooping. I would keep feeding it. The frogs I've owned have all been very good at regulating how much they want to eat. I offer food often (averaging 3 times every 4 days), and if they don't take it, so be it.