Medication can take a long time to work (see SSRI's page). Never underestimate how long this takes - it can be months before you notice the slightest bit of ease in your anxiety and it can be 6 months or more until you feel recovered (it varies from person to person). Some people though don't respond to medication for all sorts of reasons, and sometimes it can be that you particularly need an SSRI, SNRI, MAOI, TCA etc because occasionally one of those will not be suitable for you - but you can't tell until you've tried them for months - so are you on the right medication?
Someone I chat to had his DNA tested with a UK company online, which can tell him which medicine is more suitable for his body (personalised medicine). He only decided to go down this route because he's taken different types of one medicine for well over a year and hasn't felt the progress he had hoped for. His results were very interesting!!
If this is something that interests you then PLEASE TALK TO YOUR DOCTOR FIRST AND DO NOT STOP TAKING YOUR PRESCRIBED MEDICINE.
I am not a doctor and this post is just another avenue if you feel you've exhausted all others and have taken meds for a very long time.
Remember - SPEAK TO YOUR DOCTOR.