Post car crash depression, what should i do?

I'm 17 and had been driving 2 and a half months when I got hit. The impact was from behind I had no visable injurys but quite serious whiplash and my car was written off as the crash was a hard impact. I was prescribed co-dydramol for my neck pain and it started to effect my moods. I am constantly down and depressed and have been getting angry streaks. Before the accident I was perfectly fine despite suffering from depression a few years ago. I put it down to a side effect of the medication and dealt with it. Since having physio I've tried to come off my tablets to stop my mood changes but despite being off the pills for a few days now nothing has changed and I am still depressed. Is this normal or should I be worried? What do I do now?