I agree with what Cooper says on the Alpha Mindset. That helps me a lot of the time. I know everything I'm going to do hours before I go to the gym and that's all I think about doing. It ends up making me look forward to it and owning my workout and makes a world of difference to me personally. If your issue isn't anything mental, then you should take a look at your lifestyle habits and diet before you consider covering something up via supplementation. Dumping some powdered caffeine onto your tongue can help though..
From Brandon Lilly-
TRAIN LIKE AN ALPHA I want to make very clear to every one of you that I am an Alpha Male. I am not some tyrant that runs around beating his chest to tell you I am strong or the best. I let my lifting do the talking. When I am in the gym I come to work, I am not there to listen to you talk about your dog, or your spouse, or anything. I am there to train. I come to the gym to raise hell, and kick ass. When you walk in the gym you don't have to be cocky, trust me I am far from cocky, but you have to have a purpose in what you do. Ignorance is not an Alpha trait, ignorance is walking into a gym full of iron thinking you can peacefully walk through your workout. It will fail you if you approach it with that mentality. You have got to find your fire, become a war machine. Don't apologize to anyone for your dominance.