My Bearded Dragon hasnt been eating for weeks

Question
My male B.D. stops eating about 2 weeks ago no matter what I feed him.  I got him about 3 weeks ago and he is approximately 3 years old.  The temp @ basking is around 100F, 78F~82F @ the cool side, as for lighting and heat i use Mega-Ray 160W  Mercury Vapor Bulbs.  For substrate i used to have washed play sand but has been changed to non-adhesive shelf liner after he got sick.  This is kinda out of the blue for me because he was perfectly normal right when i got him, but 1 night before he goes to sleep he started to have his mouth wide open and sounded like he wants to vomit, and since then he didn't eat anything not even moving a bit.  I've been waiting for a stool sample to be collect but he is not Defecating @ all, now that he is so weak and eyes are sunken in too so I am starting to get REALLY worry.  Can you please advice me should I still wait for the sample or should i bring him to the vet right away?  And do you know what's the reason that might cost this kind of sickness?  Thank you so much!!

p.s. I am new to reptile so i don't know what kinda information you need, please let me know if you need to know anything else.  Thanks again~

Answer
Hello Wesley,
Ok.  How close is the MegaRay 160watt bulb from him?  They are safe bulbs but the 160watts do have an 18 inch distance requirement.  So, if it is closer than that to him, I recommend moving it to the 18 inch distance.
Your basking temps are only at 100 with the 160watt?  What type of thermometer are you using?  A stick on type of thermometer, a digital probe or a temp gun?
How large is your tank?
If his eyes are sunken in, he is VERY dehydrated.  Please begin rehydrating him immediately with water & pedialyte mixture.
Keep me posted on him.
 
Tracie