11 year old on zoloft - headaches?

My son has been on zoloft for just over two months. He started on 25 mg. His dose was recently increased to 50 mg. Within 2 weeks of the increase, he has had a headache, mainly on the right side of his head at the temple. He had also been on other medications for a sinus infection and bronchitis (pulmicort, nasonex and xopenex + an antibiotic). He is now off of most of those meds (except the antibiotic), so I guess I can conclude that those meds were not the source of his headache. It has been hard for me to determine where the headache is coming from, but now I am focused on the zoloft - it is the one consistent med he is still on. We have already seen an allergist (still having allergy tests), an ENT and a trip to the ER. In the ER we had a second cat scan done (The first cat scan was a month before which helped us to determine that he had a sinus infection, which have become chronic) The second cat scan showed a huge improvement in his sinuses, so we know that he is responding to the antibiotics. We have also had an eye test and have an appointment for the dentist - maybe he is having referred pain from his teeth?? He has had this headache for over 2 weeks - and less that 2 weeks before that his zoloft dose increased to 50mg. We are going to his psychiatrist in a few days to discuss, but in the meantime, my son is in some pain. When he stands up from sitting or sits up from lying down his head throbs for a few seconds and then stops, but the dull headache remains. Any advice/ experience would be MOST welcome!

Thanks - Anne