Why cant i seem to keep a job for a long period of time?

I cant seem to keep a job for more than six months .I've had about 12 jobs in 2years. . a lot of them i really donnot like.I work as a nurse aide now going to schl for my LPN programme.I need to add that i am exceptionally quiet,i do my job pretty well,a team player when necessary . . but after 6months i get tired and move on to the next job.I dont have friends,I only go out when i need to . . .sometimes my co-workers call me and tell me that am too quiet and need to talk more and join them in conversation . . thats just not me.I could stay in my room for 2days sometimes without bothering about the rest of the world.No, i dont have a boyfriend and i live alone.Is something wrong with me?