I know how it feels to be worried/nervous. In 5th grade, I started having panic attacks for seemingly no reason. At that time, it was mostly when I didn't feel right to begin with, and for some reason I guess my mind dwelled on that and made me panic. Got worse through middle school, doctors put me on zoloft for it, and now I'm pretty much grown out of them. Panic attacks are no fun.
I always found it was best to talk to someone when I was feeling uneasy or felt an attack building up. I usually end up talking to my dad about something, and I get so distracted that all the nervousness goes away. I agree that keeping a journal does help a lot. Writing down my feelings and talking it all out to my book almost helps me get over whatever bad feelings I may have. Whether it's because I'm mad, scared, sad, or just plain stressed, it still helps. Doesn't matter if you write about it, or talk about it, or heck, you can even talk about it in your head...it's just the fact that you're expressing your feelings. Keeping them all to yourself never makes anything better, usually just builds up and gets worse.
The PTSD may not be hereditary, but how you deal with stress (whether it's by choice, or just how your body reacts to it), probably is. Speaking of doctors, maybe next time you go for a checkup, you should talk to him/her about all of this. Like I said, I did, and they gave me medicine to help me grow out of it. With how hard the economy is effecting our family right now, there's a lot of stress (not to mention all the junk I'm having to deal with at school, guess that just comes with 11th grade), and it also helps me with that. I can definitely tell a difference when I run out of my medicine; seems like everything piles up on my shoulders at once. I'm not saying medicine is the answer for you (I honestly hate medicine, I like natural remedies), I'm just saying if it's really bad, the doctor may know of something that can help you.
In the meantime, keep doing what makes you happy. I don't see anything wrong with reading. It's good for you! Of course I can see why your parents may not approve of constant reading. They do have a bit of a point, there's a lot of fun stuff to do, but first you have to try it and discover it's fun. Never know, might find something else that eases the worrying
But even if you do find other things you like to do, still doesn't mean you have to stop reading. I also love to read, but I like making art and stuff too, and my birds keep me pretty occupied.