How old is your iguana? Is a girls or a boy? Have you seen any external change in his/her body? Do you suplement him/her with reptical or other supplements? What do you feed him/her? Do you keep his cage warm enough? Do you keep humidity high enough? Does he/her a proper UVB lights? . A lot of questions I know, but if we don't konw in what conditions is keep is hard to help.
Iguanas have a lot of problems like , mites,parasites, Metabolic bones desease, kidneis felure, ect....

This is a great group on Yahoo, the IGUANA MAILING LIST, that is a great supportative group. Maybe it would be a good think if you joing them a seek for advice.
Here are a couple of links that may help you:

http://www.iguanaden.com


http://www.anapsid.org/

I hope it helps and let us know how it goes, please..

You can post here or PM if you prefer , I'm really worried !!! I own an iguana myself , so far we were doing great.Now she is full of eggs, you can see from the x-rays she has between 25/30 eggs in her tummy and I'm freaking out that all goes well.