mono or leukemia ?

My son (4) was diagnosed with Mono about a month ago, but on his EBV testing it showed he was in the final stages of it and had actually already had it for about 6 weeks. The pediatrician released him to return to normal activities. He ran fever of about 101 - 101.4 complained with headaches, and sore throat, and wanted to be held. He started running temperature again yesterday, and complained with the same syptoms. I am concerned because I was reading on WebMD that a positive testing for mono, could mean leukemia, lymphoma, or other cancer's. It said that the blood test would react the same way with these disease as mono! Should I get him tested for something else?