mono side effects

I am now desperate for all the perspective I can get on this issue. My little boy, who was 7 at the time, was sick a lot last May and then all through the summer. In Aug. the doctor finally suggested a blood test and it indicated he has mono in the convalescent stage, basically meaning the infection was in the end stage. Now, 7 months later after the test, my son is still struggling. If we allow him to play very hard for more than like 1 hour he has a set back...he feels achy, headache, basically flu like. We have been to specialists to be sure everything is okay and according to the tests, he is fine. He eats pretty healthy foods and we give him probiotics, acai juice and omega supplements at least 3 times per week. He's still struggling and I wonder if I need to be doing anything else. Any input is greatly appreciated!