What Causes Petechial Rash With Normal Platelet Count?

Question: My 22 month old son came down with what was though to be petechiae from a virus. His CBC drawn 4 weeks ago was completely normal (platelets, WBC, Hgb ALL normal) but was covered from head to toe in petechiae. They are non blanching pin prick sized reddish purple (some are brownish) spots. 2 weeks after the first CBC was drawn I became concerned because the petechiae weren't going away at all! They maybe were not worse but certainly not any better. Because of this, I took him to see my pediatrician locally and she ordered a repeat CBC w/ diff. This also came back completely normal. Keep in mind he has NO symptoms. No fever, No loss of appetite, and he is acting completely normal. Only odd issue is intermittant diarrhea here and there. Not severe just soft stools maybe once or twice every couple of days but also has some BM that are formed. Ped did an occult stool test and said he had slight traces of C. Diff and E. Coli but nothing major. Because his second CBC came back normal my pediatrician is not concerned. However, now we are going on almost 5 weeks of full body petechiae! Even new petechiae are appearing as the old ones fade so it looks as if he is not getting any better. How can he have petechiae with a normal platelet count? I consulted 3 physicians through this website who were very helpful. One was a pediatrician and the other a hematologist. They both felt there was not real cause for concern due to the 2 normal CBC's.If this is being caused by a virus then how long could a virus last in him and cause this? its been 5 weeks now of petechiae! So I am hoping you can provide me more insight. Also, could a GI infection such as e coli or c diff cause his body to react with petechiae? Thank you.