Excessive Wretching on an empty stomach

My 21 month old son has had 3 Nissan Fundplications yet continues to wretch. He reciently had an Upper GI and  Gastric Empty Study completed to see if there were any more issues. The tests came back normal, his Nissan is working great and his stomach is emptying at a normal rate. The study also showed that when Jordon wretched nothing was coming up and his stomach was empty at that time.

My son wakes in the night wretching and wretches through out the day, even when he has an empty stomach but usually about 45 minutes after eating. He is on a feeding pump to administer meals (105ml) over a two hour period.

The docotors are telling me that this could be something neuorlogical but I am not convinced, please help me get to the bottom of this.