what does it mean to have a low cortisol level of 3.0 and what could cause this

Once suspected, a number of blood tests can lead to the diagnosis of Addison's disease. It is not sufficient to demonstrate low blood cortisol levels, as normal levels of cortisol vary quite widely

Cortisol is pronounced kôrtəˌsôl.

Glycogenesis is stimulated by insulin in response to high glucose levels.

Well, Pica is often a symptom in Addison's disease, which is caused by low Cortisol.

So, the only discernible connection I can see is a low cortisol level.

I see one of the categories you put this question in is "Dog Health." If you think your dog has one or both of these conditions, you should take him/her to a vet.