Right now you need to find a reptile vet. There is a vet in my valley here who thinks he knows how to care for iguanas. But he kills them with vit.D shots and injections of parasite-killers. He killed three of my igs before I put the hex on him.
Your ig needs a fecal exam, a blood test, and an x-ray to check for intestinal blockages and skeletal deformities.
OTOH, some regular vets have educated themselves and know how to evaluate iguanas' needs. i knew one, but he retired.
It's best to find an exotics vet. Mine was a one-hour drive away, and I considered myself lucky to have her.
Sometimes avian (bird) vets understand iguanas.
As it does with Brian, so it seems to me that you are not fully informed about an iguana's basic survival setup.
They are closely linked to their environment. They stay warm enough not because their bodies produce warmth, but because their environment provides just the right warmth. Their environment keeps water in them because of daily rains that run down the bark of trees, and the 80%-plus humidity. They drink from that running water. To mimic that is the best way to water them. or, draw 2 inches of 80 degree water in the tub and put him in it, even though he hates it at first. It's the tub and not the water that scares them, but all the tubbed igs seem to learn to drink that way.
Cut an 8" X 4" piece of cereal box cardboard, fold it into a V, open it so it's a roof, and lay it on the ground near the cool end. He will spend time in it. Stressed igs instinctively really need to hide at times.
Bright general lighting is needed, and at one end of the habitat he needs a UVB-producing emitter, like the Zoo Med PowerSun UV Mercury Vapor UVB Lamp. It's 100 watts, so be sure you don't overheat his cage. That end of the cage is the "warm end" (90 to 95+F.) and the other end is the "cool end" (70 to 85). Igs need to move between the extremes during the day to regulate it's digestion.
At night, igs need total darkness, not some "dark blue nocturnal light".
You need to do reading because there is so much important stuff that you need to know:
Do your iguana a big favor and read this.
BTW, iguanas do "catch-up growing".
BTW, the higher an iguana is off the ground, the more secure it feels. So try to raise his vivarium.