Along with checking all the possible physiologic causes of a screaming,
arching baby, is it possible that someone just consider it the baby's
disposition?  If the newborn were capable of talking, maybe he or she
would just be one of those people who complains alot.  My second screamed
 for what seemed a nearly continuous three year period...until he was old
enough to really let me know in great detail what was on his mind.  He's
a great kid, lots of fun, but flexibility is not his strength.  Maybe as
an infant he just was expressing (albeit very loudly and quite
frequently, including most times he nursed in the early months, which he
later loved and continued for "X" amount of time) that he didn't like the
changes, such as the light going on/off, the vacuum starting (rare
occurrence)/stopping, the sun rising/setting...you get the idea.  Is
there a risk that this will turn into blaming the breastfeeding when it
may just be nature?
Lee-Ann