Pictures will really help so we can see what kind of condition your iggy is in. I sadly lost my male iguana that I had for 14 years last winter to kidney failure. I raised him from an 8 inch baby to a 6 foot beast. Plan on build a much bigger cage in the future. They enjoy a lot of room.
As for diet I recommend a varied one of lots of healthy greens like spinach, kale, dandelion, violet, & hibiscus leaves, mustard and collared greens. Avoid lettuce! Grated carrots, squash and zucchini are also good. They enjoy some types of flowers like hibiscus, dandelion, geranium, viola, and pansies. You can offer fruit a couple times a week to the diet like grapes, strawberries and bananas. Sprinkle some vitamins and calcium on the food a few days a week. Good luck with your iguana!