First of all, let me see if I have this right. You have frogs of different species housed together? If this is the case, separate them immediately. There are a few reasons for this. First is cross contamination, many amphibians species produce toxins to protect themselves, while at the same time all amphibians have porous skin. So keeping multiple species together means that they are poisoning each other. Second, most of the species in the pet trade are wild caught and come with their own parasites and pathogens native to the land of their origin. So what can happen is cross infection, animals infecting other animals that would not have any immunity to foreign diseases. Third there is environmental needs. Not all species have the same requirements, so it is just about impossible to house multiple species together from around the world happily. Someone's needs will not be met in this situation. Then there is stress of being kept with other species and stress kills.
Ok now on to what may be wrong with your frog. It may be a sore from rubbing its snout on the sides of a tank or on the top of it, but I really can't diagnose the problem without actually seeing it.