iggy not growing real well

[spavdude2400]

i have had my ig since july 1st roughly when he was 11 inches. well now its gonna be almost 4 months soon and hes like 12.5 right now. i have proper uvb/uva lighting, heats good, amb temps good. viv's good. i usually make him a salad everyday with at least 2 diff greens turnip or mustard or whatever and ill put chopped parsnip in it or acorn squash or whatever. i have done. i dont know whats wrong. i have tryed vitamins for like 2 months now that aint doin it. i seen some growth charts of baby igs growing like 2 inches a month at least with a max of like 3 to 5 inches a month sometimes. its really gettin annoying now. i watch him eat fine. the only thing is we got him from a carnival vendor who was giving them away as prizes. he had at least 30 in a cage. but yea what cha think?