I have an odd, completely life and mind consuming phobia, and it seems so irrational but I can't help it.?

For about 3 months now I, without any break, have been consumed by a fear that everyone potentially is out to get me. Like that people either want to kill me or at the very least do bodily harm to me. I swear to you that I have been thinking of this fear for 3 months now every minute and hour of the day. I could b reading a book & still these thoughts pop into my mind while reading or even talking to a friend of mine on the phone. I draw up scenarios in my mind that would seem impossible 2 others but possible 2 me in which people harm me or r plotting to harm me. I am 19 and I am already beginning to go insane. Like actually insane 2 the point where I am actually avoiding as much contact with the outside world as possbile besides the friends and family that I trust. I fear that old enemies from the past are plotting to kill me in the future. It is taking over my entire life. I won't even go places much anymore unless I'm familiar with them. Is this normal? Should I get help? Advice???