My 13 yo son has been on 50 mg of zoloft (sertraline) for 3 months. Having rashes from the sun & other issues. Can we just stop? Can't get a hold of his dr.

Reduce the dose. It is best to reduce the dose by a half until you can reach your son's doctor. .
Not advisable. Sudden stoppage of psychiatric drugs may have undesired effects fir which a weaning process is generally advised. Until you get in touch of his doctor, try to lower the dose some, by -20% at a time.
Wait until tmw (Mon) In meantime, stay out of sun. 50mg of Zoloft (sertraline) is on the low side of dose range, so you could probably just stop but w/o listing more side effects (http://www.drugs.com/sfx/sertraline-side-effects.html) aside from rash from sun, I would recommend against it. Instead, call office tomorrow (Mon) and tell doc what's going on. S/he may want him to try lower dose or different medication.
Zoloft (sertraline) Effects. You are very caring mother! Zoloft (sertraline) is a medication for depression and anxiety. Treatment for your son needs to include Individual therapy, Family therapy, Marital assessment and therapy if needed, and Medication. Dosage of Zoloft (sertraline) needs to be monitored and adjusted based upon severity of depression and anxiety by a Psychiatrist.Rash is not a common side effect Call Doctor covering for Psychiatrist.