It sounds like you could use the help of a therapist.
In the meantime, self-help books can be really good if you like reading. Do you have other things happening in your life (or that have happened) that you see as critical events in your life that had an effect on who you are today? Think about them and try to find self help books on the topics.
I would start talking to anyone and everyone. At the grocery store, find a small older woman that is looking at an item or trying to get something off a shelf and say something like, “I see that you’re trying to get x, can I help you with that?” Or “I see that you’re looking at y. I’ve never bought one before. How would you cook it?” I say pick an elderly woman to take attraction out of the equation, but can also do this with men.
Get back into talking to people, and sharing and learning about their and your experiences.
It will be hard, but if you pick someone you’re not attracted to, like the elderly man or woman, it can help you feel more comfortable with speaking to people in a relaxed situation. At the least, maybe you learn something new about a vegetable or get a new recipe.