pain that radiates from sternum

My husband has this pain that radiates from his sternum. He says it fills like being kicked in the chest, only intense. We have been to 2 gastroenterologists, tons of blood and urine test through his endochronolgist, {he has hypo-thyroidism},all come up negative for cause.  We saw a neurologist today who said he would do a EEG and MRI, but he didn't think it was neurological.  What's left??  My husband is currently on Nuerontin,and a Fentanyl paid patch to cope with the pain.  any other suggestions?  I thought maybe is was his Vagus nerve, but the doctor didn't seem to agree