What you are describing is not introverted... introverts can actually be very engaging conversationalists, we just have different styles (eg, we are more likely to enjoy a one-on-one intellectual discussion rather than small talk in a party setting).
For us introverts, it gets to be a bit insulting when people refer to being an introvert as a character flaw... it is only a different style of relating.
What you are describing is difficulty in socializing, enjoying people... social anxiety and dissociation.
Your personality hasn't changed, you are just struggling (and hey, there is nothing wrong with being an introvert!)