Wow, a lot of questions: Here goes...
I cultured regular Pseudomonas aeruginosa at age 10, hence the first round of IV antibiotics.
Previous to that I had cultured staph aureus, treated by oral antibiotics.
These days I usually culture 1 or 2 strains of mucoid P.aeruginosa.
(I don't know if I picked these strains up or if they evolved from my first infection).
I get IV tobramycin and ceftazidime (fortum) about 4 times a year.
Recently changed to Cefapime as ceftazidime doesn't work any more.
Physio wise, as a kid up to the age of 16/17, I coughed up hardly anything.
Back then the regime was postural drainage and clapping the sides and back.
I always did loads of exercise, not because I had to, but that's just what all the other kids did.
These days, because I cough up so much phlegm, I have to tip up and use postural drainage.
Apparently this is very old school.
But, for me, it clears 90% of the phlegm in about 10 minutes.
I also find somebody clapping me on the back, while tipped, helps get the last 10% out.
So this is peculiar to me and doesn't work for most people with CF, from what I hear.
(probably cos they don't cough up much phlegm).
In my 20's and early 30's I played a lot of soccer and I always found I coughed up much less phlegm the day after training practise/soccer game.
Again, I played because I loved it.
I never stuck at running because I disliked it.
So I guess, finding something your son likes to do is important.
Try him out at everything: tennis, Golf, hill/mountain walking, rowing, he'll find something he likes I'm sure.
Of course exercising is easy when you have the extra residual capacity to exercise easily as I did back then.
Now, as my lung function has dipped under 40%, I find it incredibly hard to exercise.
Walking on a flat is fine, but going up hill or breaking into a jog is next to impossible.
Not to mention frustrating...
Finally, weight wise, I always struggled to put on weight as a kid and into my 20s.
Now in my 30s, I find it easier to keep the weight on, (I suppose similar to most 30 somethings).
My parents tried and tried to get me to eat, so much so that I hated meal times.
Of course I liked junk food but back then it was doctors policy to eat healthily (and even fat free).
Now, we all realise (and laugh about it) they should have been trying to shovel chocolate bars, burgers, fries, cola, etc down me
We CF-ers need to embrace the obesity epidemic.
So now I eat normal healthy meals plus all types of high calorific food (be that burgers, fries, biscuits, cake, high cal drinks, whatever).
My BMI is 23, about as good as it can get, I believe.
And don't worry about your son's size, if he gets enough calories into him, he'll more than likely grow to his full height.
I'm about the same height as my Dad, although puberty was delayed, all my friends shot up at 14yo, while I didn't start growing til about 16 or 17yo.
But I passed most of em out in the end...