Im always nervous when people try and talk to me

Im always nervous when people try and talk to me. When I get really nervous my face and neck come up in red marks which is really embarrasing. I find it really hard to go out with friends as im scared my marks will come up. Ive got a bf but im to scared to go anywhere with him. Im finding in really hard to keep a job as my red marks come up when im nervous or get a bit stressed. Wats wrong with me? :(