To know if I have a mental disorder.

I've been this way ever since I was young. I overthink the smallest things till it ruins my day and I tend to dwell over what has happened till I get headaches. I dread scrutiny in social situations and try to avoid them altogether, sometimes I go when my friends are as well but I don't always enjoy myself because I'm constantly worried about what everyone is thinking of me. I second guess myself all the time and I'm never comfortable speaking my mind around anyone let alone trusting them. I don't get along with my parents at all because I find it difficult to say anything to them. I never feel as though I turned out to be what they wanted. I despise confrontation and sometimes I break down entirely and start to apologize even before I can try defending myself. I don't even know what my own personality is because I keep changing it based off the people around me. I'm scared of what this could do to my future corporate life. I'm so nervous at times, I get nauseated and short of breath.