Hi and welcome to the forum
No it's not normal. It could be the frog ate something like gravel or a snail and that is blocking part of its intestine. Or a growth like a cyst but these normally take a few weeks to grow to size.
I would take it back and swap it for another one.
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Make sure your water quality is good (no ammonia or nitrite, and nitrate below 20ppm at all times).
If the water looks cloudy, and it looks a bit milky cloudy in the pictures, do a big (75%) water change and gravel clean the substrate.
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How long has the tank been set up for?
If it's a newly set up aquarium, keep feeding down to 2-3 times a week and do a 75% water change and gravel clean the substrate 4-8 hours after feeding. Then monitor the ammonia and nitrite levels and do a 75% water change any day there is a reading above 0ppm.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
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The following links have information about frogs and might interest you.
Here's a little guide I've written for a few forums that may be of use to you(it also has a couple of quotes from a fellow frog keeper) ; Common Name : African dwarf frog, congo frog; do not confuse this frog with the African clawed frogs(these will get much bigger and will eat small fish)...
www.fishforums.net
I found this incredibly informative care sheet on African Dwarf Frogs and I wanted to share it with everyone here. I see a lot of bad information going around when it comes to African Dwarf Frogs so I hope this helps people understand the proper way to house and feed these wonderful little...
www.fishforums.net
allaboutfrogs.org