I have always been very self-conscious about the way I look.
I think most people are to a certain extent. It is defined as being a heightened sense of self-awareness.
Yes, I would definitely agree that most people experience some self-consciousness at some point in their life.
Most people experience a feeling of being unpleasant, especially, when they notice they're being watched. Like everyone is looking at you
Yes It's funny we think that way because in all likelihood, people aren't really looking at you.
Some people can even be habitually more self conscious.
I would think outside influences would affect the level of self consciousness too.
feelings of self-consciousness are sometimes associated with shyness or paranoia.
Impairment.
When feeling self-conscious, one becomes aware of even the smallest of one's own actions. Such awareness can impair one's ability to perform complex actions. 
Adolescence is believed to be a time of heightened self-consciousness. A person with a chronic tendency toward self-consciousness may be shy or introverted.
Psychology.
Unlike self-awareness, which in a philosophical context is being conscious of oneself as an individual
Self-consciousness
Self-consciousness is a heightened sense of self-awareness. It is a preoccupation with oneself, as opposed to the philosophical state of self-awareness, which is the awareness that one exists as an individual being, though the two terms are commonly used interchangeably or synonymously. An unpleasant feeling of self-consciousness may occur when one realizes that one is being watched or observed, the feeling that "everyone is looking" at oneself. Some people are habitually more self-conscious than others. Unpleasant