I think you've captured Giny's character very well.  You show her mood swings (she loves him--she loves him not--she'll leave him--she'll leave him not)--definitely the way pregnancy works. 

I have a little trouble believing in your Harry though--only visiting long enough to get the poor girl pregnant.

You have  a nice way with a phrase.  I particularly like:

"...I am determined never to regret anything we have done together..."

"...I feel like a terrible mother for only wanting you..."

"...Tom wants me dead because it will break you."

"Still waiting for your stuborn son to make his way into the world." (tee-hee!)

You give Ginny and Harry's history in bits and pieces thorugh out Ginny's writing.  I like this much better than lumping it all at the beginning like a news article.   She also glosses rumors of the progress in the hunt for Tom.  Both of these devices add interest and drive the story forward. 

 I'm not very good with songfics.  They are hard to write I think.  The hardest part is finding the right song.  I think you picked a good one for your story.   But when I read one, I like all the lyrics to fit well with the author's storyline.  Yours does most of the time, though not always.  F'rinstance, the song talks about crying and screaming and tears, but then you say Harry and Lils are 'stoic.'  And when I read 'resonating life', I expected to hear more about Harry's bravery.  But that's just me.

So, nice job for your first songfic.