A speech therapist could help. Also, perhaps acting classes, public speaking classes or Toastmasters, or even just a helpful nudge from a trusted family member or friend would be useful.
I went through years of acting classes and public speaking classes, and they helped me learn to deal with inflection, register, and eye contact when speaking to a group. Now all I have to do is prepare mentally for a few days or so and I can handle such situations. In all other social situations I'm hopelessly lacking in affect, from body language to intonation.