Why is my 12 year old being sick everyday

[Mers1]

My son has been bullied in the past and had suffered with headaches and stomach aches for well over a year. We have moved him to a different school and he is now very happy.  The only thing is he is still feeling and being sick every day, he is very over weight but is very stubborn and won't eat very healthy.  We have had lots of blood test done, an ultrasound, stool samples, Mir and they can't find anything.  The doctors are putting it down too anxiety but I'm just worried they are wrong, as he says he's happy in school and just don't know what to do.  I hate seeing him like this.