It's hard to draw a clear line between biochemistry (in the sense you are using it - short term changes in your brain's chemical make up) and your brain's long term state based on genetics. I always strongly disagreed with this position until I read this piece by David Eagleman. 

He talks about how Charles Whitman (who went on a shooting rampage at the University of Texas) was a completely normal, straight A student until months before the incident. He wrote in his diary about a weird sensation coming over him: an insurmountable urge to kill. He asked to donate his body to science to examine his brain to see if anything had changed. Sure enough, after killing 13 people and himself, scientists found an enormous tumor pressing on his amygdala.

It's easy to have some forgiveness for Whitman, as we can somewhat sympathize with his situation. If it could happen to him, maybe it could happen to us. That's one end of the spectrum. But Eagleman raises another point - what's the difference between a tumor changing his brain and someone else whose brain is naturally predisposed to bad behaviour. I like to believe in free will, but the evidence of the correlation between brain chemistry and behaviour is pretty strong. I'm struggling a bit with where I'm comfortable drawing the line.

I try to tell myself this but I always end up beating myself up for not being able to keep pushing anyways. I look around me and everyone's sleep-deprived. They still push on, though.

It's not a healthy way of thinking about it, but I can't help it.

Lots of things change our biochemistry.  Air, water, smoke, coffee, prescription drugs, etc.  But, the remarkable thing is that our biochemistry also changes in response to our envioronment including sounds and music, cramped versus open spaces, lightness and darkness.  This time of year people in countries in the Northern Hemisphere suffer from seasonal affect disorder -- because their mood (e.g., caused by biochemistry) changes in response to the reduced hours of light during the day and increased inclimate weather.  Understanding all of that and adopting a holistic view of your body and controlling it is the challenge. 

You are completely right, however.  Movement, exercise, quality sleep, and eating healthy foods are all ways to control your biochemistry in a positive way and maintain an upbeat and positive mood.  In addition, meditation, prayer, yoga and other introspective practices also provide greater/deeper insights -- perhaps even insights into the soul and Nirvana.