Sounds like your frog is stressin' (take it to a vet for sure). If your frog is an adult or even a larger juvenile, then anything less than a 20 gallon terrarium is really small. Also I would ditch the fake plants for a bunch of live ones. The more plants the better, not only will they make your frog feel at home, but they also provide humidity and a place to hide out if they feel like it.

With live plants you will also need to change up your substrate. My standard substrate mixture is 2" of clay balls, another 2" of coco husk, and I usually cover the top with sphagnum moss, or some other type of moss to prevent the coco husk from sticking to the frogs.

Here is a pic of my terrarium setup for my 2 American Green Tree Frogs (aprox 23 gallons). This is the only terrarium in which I have fake foliage (I use it as extra cover because these frogs are really shy and almost always want to hide) Other than that I have 3 live plants on the ground level with their water dish, and two live plants on the upper level (one being a pothos that grows down to the lower level) as well as a patch of live moss.