What Do I Do?

So I'm having a rough day, my oldest son is being very defiant, and even took off today on his bike, saying he was running away (I knew he wouldn't so wasn't too worried, and wasn't surprised when about 15 minutes later he called from my sister in law's house crying wanting to come home).

I don't think his meds are working for him, he is on 10mg of Prozac every morning, and it was working really well for awhile, he was like a whole new kid, calm, accepting, and generally, well, normal. But over time the meds seem to be losing their potency and he is going back to his old ways.

I know I have never posted about his old ways, but let's just say, you don't want to know a kid like that. There have been days when I was sure he was either going to kill himself or someone else, and I just don't know how to deal with him when he gets like this!

I have had one counselor tell me she thinks hes got some Cognitive Delays, but he has had evaluations, both psychological and developmental and no one noticed any signs of that. I have researched it on my own and I think she's full of shit and just can't stand to be wrong.

Days like today I feel like a complete failure as a mother, I wasn't able to protect my child from whatever it was that happened to him, whatever has caused this anxiety, depression and general behavior problems. My child talks about killing himself, when he is being punished, He tells me that the reason he can't go play outside is because I am afraid he's going to kill someone... HOW do you process something like that? HOW do you DEAL with something like that? WHAT IN THE WORLD am I supposed to do?

I have spent the better part of today crying, and wishing there was someone else that could deal with him because I just can't do it anymore. I love all four of my kids, but I feel as though I have done everything I CAN do, there is nothing else LEFT for me to do! I just don't know what to do