5 months and where did my happy baby go?

AHHHHHHH! We have a whole new Shelby now!  One that cries frequently and long, one who doesnt like to sleep through the night.  Our whole routine is off and I am tired.  I wish I knew why,,,  Is it the gas? The teething?  Is she hungry,..  :-(  Here i sit at 3am with my unhappy, non-sleepy baby..  I sure hope it passes soon!