I would call the vet just to see if they can give you some advice over the phone. Since he hasn't eaten in two weeks you need to get food for him and force feed him. They sell that at a vet or you might be able to get it at a pet shop. Its in a liquid form that you have to syringe in his mouth. If its a calcium problem you have to dust the crickets every other feeding. Once a month is not even close to being enough. Crickets are pretty much all phosphorus, you also need to get a calcium powder that is phosphorus free. Phosphorus actually blocks absorption of calcium, so if you have powder with it in there you are doubling the chance of him not getting enough to begin with. I would continue with the drops but he needs to get food in him.