Social anxiety or something else more serious. who can diagnose it?

Psychiatrist: A well trained, experienced psychiatrist is the short answer. Since the range of symptoms from discomfort to paralyzing anxiety in general to specific interaction or even severe avoidance, a skilled & thorough evaluation should clarify what is experienced as well as the underlying cause. So the difficulty may range from incidental or relatively contained to initial sx. Of schizophrenia. Serious!

Psychiatrist/PCP: A psychiatrist will be able to tell you if your anxiety is due to a medical conditon or is social anxiety disorder.