17 yr old male. Had depression. Anxiety and ocd. He's on Zoloft and wellbutrin. Would it be wise to try pristiq (desvenlafaxine)?

Not necessarily. Pristiq (desvenlafaxine) is a seratonin reuptake inhibitor such as Zoloft., so it does not necessarily have more to offer than Zoloft.
Anxiety and ocd. First you need to know that wellbutrin (bupropion) is not effective in OCD and may actually make it worse shown in a study by vulink nc in 2005. Second please know that 30 %of all patients with OCD show insufficient improvement with state-of-the-art treatment. So before proceeding with treatment please have a test done by assurerx to determine genetically if his metabolism responds to the medications.