anyone have advice :(

thank you in advance to any who responds or helps, it really does make a difference and I always use your advice.

ever since I got my new corporate job, my already existing social anxiety has rocketed past my control. (to give some visuals) for example, when my new co-workers walk past me and say something as simple as "hey" I automatically get nervous. I do respond, but then I immediately look down. Today my coworker walked in around 2PM and I wanted to be casual so I was like to him "where you been haven't seen you today" and he responds "not here?" with the most serious face, which automatically brought my self-esteem to a 0. I am the front desk receptionist at this job so everything is constantly walking by me, i just wanna act natural but it never works out without me looking like i'm trying too hard.