Just bought a baby iguana and he died?

I bought an iguana less than 2 weeks ago..probably about 3 months old..I have everything for him..a 40 gallon tank, under aquarium heater, heat lamp, uvb/uva light, vines, ect...he was green and ate very well...yesterday he started to look a little more brown than usual...but still ate well...this morning, he ate but looked even more brown...this evening he was limp and had ped away....??? any suggestions?