Green Iguana Society Message Board: Bad Uvb lighting and growth

I'm a first time iguana owner and I think I've been over stressing about his health and growth. He's 4 months old, but only 4.5 inches from head to vent. 16 inches from head to tail. I've raised many bearded dragons, but he is something else.

He's in a 55 gallon tank, with plenty of climbing space. His basking spot stays at about 90°F and his humidity stays at 80%. I bought a reptisun Uvb bulb which I'm going to replace tomorrow for a tube. He's fed many different foods including collard greens, beet greets, arugula, squash, peas, and a few fruits now and then.

What on earth am I doing wrong? I feel horrible every time I measure him and he hasn't grown.

It has been very cold outside, could the season be affecting his growth? Am I missing something? And finally, if I can finally get it right, will he be to grow normally from now on?