It takes most acne treatments 2-3 months to work.
AdoxaAdoxa
Adoxa ck
Adoxa tt is a form of doxycycline. It works best of milk is drunk a couple of hours before or after taking it, but it isn't necessary to avoid milk altogether. As for sun, most patients who take doxycycline have no problems in the sun as long as they take appropriate precautions like using sunscreen. I'm not sure where you live, but in colder climates there isn't going to be enough sun to make a difference in this regard for some time. You should discuss these and similar matters with your son's dermatologist.
Take care.
Dr. Rockoff