Suggest Treatment For Glandular Fever With Abdominal Pain

My 16 year old son has had glandular fever since November with typical symptoms. He still has persisent abdominal pains, diarrhea, tiredness, aches and occassional dizziness. He is only managing about 5 hours in school over the week because of this. His GP has done more blood tests.... coeliac (as dad is), liver, kidneys and FBC. Is the persistence of these symptoms typical with gf?