Hi and welcome
perhaps your system does better on the lower dose? Also have you considered that it may be the combination of the two drugs that is causing a problem?
From my experience with both son and dh who both have OCD with their Tourette Syndrome, meds can sometimes intensify the problem they are supposed to be helping, so do talk to your doctor about the effects you are noticing. Both of my family members now use supplements more successfully to help their OCD as the side effects from the meds just wasnt worth it.
Have you considered Cognitive Behavioral Therapy? Trained psychologists help with this and it is very beneficial for OCD
We have some helpful info on it and other OCD stuff on our sticky thread above here
http://neurotalk.psychcentral.com/thread1395.html
hope that helps