Strenuous work environment

Just found out that I am 4 weeks along and I am nervous because I work 45 hours 5 days a week at a job that requires lots of standing, lifting crouching and pushing/pulling objects. I have a doctors appointment coming by the end of this week but how soon should I tell my job I am pregnant to protect the health of my baby and myself ? Any ladies ever been in this position before? Any advice helps!