Is this being kept aquatic?
You should get a test kit if being kept aquatic. 95% (or more) of the time problems with aquatic animals are a result of bad water condition. This is not something that can be seen by the naked eye nor is the behavior of other animals meaningful here. One animal could be more stressed to begin with and that stress can be further enhanced by bad conditions. If in the USA, the cheapest test kit is the API Freshwater Master Test kit. You can get it at any big box pet store and most local pet stores as well as online.
In the meantime, start doing 90+% water changes. Do them once a day until you get your test kits in.
Is the newt eating at all? Again, pictures would be very helpful here.
Good luck,