Why do people stare at me blankly and go “what?” every time I talk?

For context, I (23F) work in the sciences and often have to present my research to an audience. In both casual conversation and while presenting, I often struggle to feel I am connecting with my conversation partner (especially if they are a stranger) and audience. I do get anxious, so it makes it worse when I speak and get met with a blank stare. For example, if I am asking someone a question, they often squint their eyes and go “what?” Or just stare at me blankly. The other day I asked a guy on my apartment elevator if he wanted me to scan him up to his floor (he was clearly struggling to get his reader to scan and threw his hands up in frustration). After I asked he kept asking me what I said, and then these girls started laughing at me and said “what is she saying?”. I was really embarrassed and got off the elevator quickly. I heard them say “wtf” behind me. I have a very slight Southern accent I guess and just moved to the Midwest, but this has been happening to me for years. During a recent presentation of my research, an audience member in my department and her boyfriend who was also in attendance grilled me on my research, which is totally fine. However, they didn’t ask questions to any other presenters and their questions for me were almost repetitive and there must have been about 10 of them. Every time I would answer they would say “hmmm” and my advisor afterward remarked that it was strange, but maybe just to assume the best. I guess I’m just confused on why this is happening. I don’t have many friends and have always struggled to get along with people in social settings. I am kind of ugly and get negative random comments on my face a lot, and people staring at me not understanding what I am saying makes it more difficult for me to overcome insecurity. Does anyone else struggle with this and know why I might be getting such weird reactions when I talk?