Bearded dragon help please?

I bought a bearded dragon yesterday and hes underweight. He has ate 6 medium sized locusts and about 6 mealworms. Should I keep feeding him that or is there something else I should buy. I did buy a pinkie but when i fed it to him i did it after it ate the 6 locusts and he wasnt interested so I will try it tomorrow before I feed anything else to him. So write please. Also he said to me that because hes desert animal he dosent need water, so he hasnt gave him any water apart from his 2 weekly bath. So I tought him how to drink out of his water bowl and he drank the lot :).