I'm the same way dear. I have 5 weeks left and it seems every day I'm on the verge of tears for no reason. There is depression before birth, it's just not as 'advertised' as POST partum depression.
Try a cup of hot tea with a little bit of sugar. Just sit there and sip it and remind yourself that you're gonna be someone's mother in less than two months! Think of what they are gonna look like. Will they have hair? when will they laugh? Think of the positives, shove those nasty thoughts out.
If it does get really bad (thoughts of suicide type bad), talk to your doctor, cause that's really serious stuff.
Good Luck Sweetie! I hope you feel better!