How long have you taken SSRI's and -- this will frustrate you even further -- are you sure you need SSRI? Some individuals need the opposite or something different altogether. Not everyone's DP can be treated exactly the same. I wish we all had the same pill and get rid of this thing but realistically speaking, everyone's biochemistry is different -- everyone.
There's gonna be a lot of stones on your path and many hurdles but you will find what will work for you.
Also don't be fooled by feeling relief and associating that with no anxiety. Anxiety can stay dormant and even affect you while you sleep.
To truly eradicate anxiety, it takes more than just a pill, sorry but that's almost always true.
Diet, exercise, mindfulness and laughter will definitely be the main contributors to your recovery.
Then again I could be wrong...or right.