For one thing the time frame is all wrong.  “Heresy”, as Prof Ehrman has pointed out in the past month or so, means literally “choice”, choices in belief.  These choices probably started occurring right after the death of Jesus.  By at least the time of Paul (writing in the 50s and earlier which would have been only 20 years after Jesus) we start to read about different beliefs.  Paul complains, in writing, on several occasions that outsiders (he calls them various things including, perhaps sarcastically, “super-apostles”) are preaching ideas to his churches that are at odds with what he believes and preaches.  I’m not one of those people who can quote chapter and verse so if you want specific examples ask here and I’ll give you some, otherwise you can find them yourself.  Look in 2 Corinthians and Galatians although they can be found in other places.  The word “heresy” didn’t come into common use until the 2nd century (100-199AD, so less than 200 years technically speaking) when Irenaeus started tossing it around (he was the author of a work called “Against Heresies”) although other Church Fathers described heresies, perhaps not with that name, earlier than that.  The earliest heresies were seen as those beliefs and ideas which were tainted by Jewish beliefs.  As Christianity spread and became more and more of a universal non Jewish-centric religion the Jewish interpretations would have been seen more and more as non-Orthodox.

I came across this blog post by Larry Hurtado today that you might be interested in:  ** you do not have permission to see this link **, in which he discusses a recent book on the topic.