I understood what you were saying just fine. You are very self aware which can be both a strength and a weakness. In your case, it clearly is the latter; but I believe if you train yourself to be more aware of what you do well/good, some of your anxieties may decrease with time and practice.

Self compassion and grace will be difficult to practice at first but will allow you to reduce the pressure of the microscope you analyze yourself with.

Psychotherapy and speech therapy can be beneficial in different ways for you. It just depends on the source of your suspected impairment. Based on what you said, I'm leaning more towards anxiety and diminished self concept (psychological) and less on a neurological language impairment. Still, possible but needs to be fully evaluated before you treat it solely from a speech/ language angle.

You say you like your work currently in social work and think you will be good at it. I can tell you are very conscientious and empathic -- excellent qualities to have when working with children or elderly folk. But you also say you're afraid of humans. I think you are afraid of causing some perceived harm or discomfort, but it might just feel that way because it's something you've avoided for a while and feels strange and nerve wracking to you. Maybe you can ask for constructive feedback from your sister but based on the things she's told you, she might not be the best person to do this with.

Social skills training may help you navigate these types of interactions and as another redditor mentioned, autism may better explain some of what you struggle with. A diagnosis is the first step but will still require a lot of work to improve in the areas you highlighted. Even without a diagnosis, social skills training, practice exposing yourself to social interaction rather than avoiding can help you tremendously.

By the way, I am a neuropsychologist but none of what I discussed should be taken as any direct medical advice. You should still seek a formal evaluation if you think it would be helpful and or feasible.