Have Reptile Questions? Ask a Reptile Vet for Answers ASAP
Do you have a thermometer in the tank to monitor temperature? glass can hold heat in and its possible that the tank is warmer than the room it is in. Glass also holds in humidity. Russian tortoises do best in dry environments. I would recommend putting him in an open plastic tub or a constructing a tortoise table like this one: http://russiantortoise.net/tortoise_table.htm
If this does not help then your vet can perform blood work to look for issues that wouldn't show up on a musical exam like kidney disease.
Yes, its true that babies need more humidity than adults because they will dehydrate quicker, the ideal range for humidity is about 50-70%. Much less than some other species that need up to 100% humidity at times. You may want to consider a drier environment with humid microclimates such as those that can be created by keeping an area of his enclosure more moist than other areas. This can allow him to regulate the amount of humidity he needs. Also, if you are not giving him a supplement perhaps this is what he is missing. the most common deficiency is calcium but others are important too.