cephissus sounds like your probably overtraining. try staying away from failure.
Last week I decided to cut my volume in half, essentially. Instead of hitting everything twice a week, I just do roughly the same workout but only once per week. Only lifting MWF and like one or two exercises per muscle group a couple top sets max. It might sound funny, but I can't even go to failure most of the time. My muscles don't even feel like they're working even though the weight is moving, and I just have to stop once my joints start hurting.
If "overtraining" is the problem, I would expect an improvement after dropping to once a week. Just got back from the gym though, and everything went even worse than last week!

Today was the worst I've felt in a while. Absolutely nothing worked. Muscles completely dead. Nevertheless I'll stick to this reduced training load for another month or so and see what happens.
I've heard of people "overtraining" for long periods of time, and then having to take months off or even years to recover. I really don't want to even think about that, but it does seem like a possibility. I hit it very, very hard for a long, long time before wising up. I've never actually met or talked to anyone who had this problem though, so I don't know how they diagnosed themselves.