Ah yes, hypochondria, i have the same problem (although it's been getting better). I've found that it helps to talk to people about it, because others can help you assure yourself that you're not actually terminally ill, which is the case in the VAST majority of times. None of my hypochondriac flailings have ever amounted to anything besides excessive worrying, which is beginning to lead me towards "i won't be in doubt when i'm actually sick". And that's a helpful thing too, because again, in the vast majority of cases, you really won't be in doubt when something is afflicting you.
Granted, you've had a bad streak of misfortune with complications, but that doesn't mean everything is going to turn out like that, especially when it comes to the cancer risk of x-rays. The risk is MINIMAL, especially for a young and otherwise healthy person like yourself, otherwise it wouldn't be such a widespread thing to use.
Basically, you just have to try your damnedest to not worry about it. I know it's REALLY difficult, i've actually worried myself physically sick before, but it can be done, and this comes from a guy who otherwise just worries too much about everything. Also, what Poo up there said is sound advice, i've generally stopped checking for such things because i KNOW what will happen. The amount of times i've feared heart attacks, lung problems, appendicitis and what have you is beyond my ability to count, yet none of these have ever actually happened. The worst offender for me right now is my gut, which has been acting up for months now, but i remain alive with no real complications besides the odd day off from classes.
But yeah, long story short, you'll be fine. If you feel anxious, speak to someone about it, it can be really helpful.