nobody was saying that, if he is a male he will get bigger unless something will stunt his growth, say mine is a bit over 4" at 9 month. he is small and will probably be never as big as average male, but I love him the same genetics of course has influence too as well the fact that they all grow at differently. to add to this- I'm pretty sure you have a female,.

If I were you I would take the advice given and change completely his tank ASAP, meaning proper substrate and water bowl. that would be a first step. then you need to make sure temps and humidity stay at proper levels. then start feeding properly, I would go for everyday feeding and as much as he would eat for now and see how it'll go. You never mentioned if you are using Ca/vit3 supplements, you have to use it every second feeding and once a week multivitamins. It is crucial at his stage of development to get proper nutrition and supplements. Use only de-chlorinated water.
follow the advice on feeding more nutritional food then crickets, but keep in mind variety is important too, you can give once in a while hormworms, butter worms, wax worms, pinkie ( no more then once a month), but as a staple - nightcrawlers and roaches.