Little Boy is Very Sick- Ask Dr. Mona

Question for Dr Mona:
Little boy REAL SICK! My little guy is sick He has been coughing, runny nose and a fever off and on since Jan. The last three weeks he has been complaining of his legs hurting and was limping I took him to the doc over it all and he said he probably a virus and his leg is fine just him being a three year old. Now he is complaining of all the above plus his throat, and stomach. I have been taking him to the doctor frequently and two days ago he started running one of 105 and having fever dreams. I took him to the ER and they said it was a fever dream and sent me home telling me to follow up with his regular dr. My sons dr is very concerned and one of the top pediatricians in the area. He ran more tests to try and figure this all out and told me he is stumped and this was a very odd case. All of his tests came back okay including nose swab, urine test, blood work (including cbc), and x-rays. Please Help I'm scared

Check out this video for Dr. Mona's answer!
If you have a question for Dr. Mona, post it in the 'Comment' section on her channel here:
http://icyou.com/channel/ask-dr-mona