What is Wrong With My Baby?

I am at a loss.  Not sure what to do about Mary Katherine.  She is almost four months old...and ever since she was hospitalized for RSV, she is not the same. She breaths fine...and her congestion and cough are gone...but something is just not right.  She doesn't nurse with any sort of gusto, she cries when she nurses or takes a bottle, she chews on her hand, she will only sleep for about 20 minutes at a time (except at night), and becomes hysterical crying for long periods of time.  We took her to the pediatrician who started her on Zantac two weeks ago for acid reflux...but the behavior continues.  I keep checking for teeth...thinking that she could be teething...but there is nothing.  And she is hysterical when she cries...I can't imagine that teething would cause her to cry the way that she does.

It is so upsetting!  It just makes me sick to hear her crying like this.  She is in pain, I can tell....but when I take her to the pediatrician's office, everything is fine.  I don't know what to do.  She was such a sweet and gentle and quiet baby until three weeks ago.  I am worried that something is really wrong with her.  My sweet little girl....I wish I could help you!