Gaining 6 grams in a month and a half is not what I would call gaining weight.

Here is something that has been proven to work

Get a 6 quarts tub, use aspen bedding, use a 6 inches flower pot saucer as an hide, provide a hot spot of 86 degrees.

Once you made the switch wait a week and offer a live hopper mouse in the tub once a week.

No handling until the animal eats with consistency.

Keep the animal in that tub setup until it reached 150/200 grams

At this age and size the animal should be voracious and right now it is not and at this size it could go down the hill very fast.

The main issue I see here is the lack of security which is THE most important thing for an hatchling that size (this is the average hatching weight out of the egg). Some do not do well in class enclosure especially that big even if cluttered up, making changes to addressed the security issue will be one step in the right direction feeding the appropriate size prey will be the second step fuzzies are in no way suitable.