How focused are you?

Ever since graduating, I'm grinding 9-5 with overtime during crunch times. Im a software developer.

I'm definitely learning a lot from my job. There are lots of skills I've picked up. Technical and non-technical. However, I feel like my mind is less focused. During work I commit to staying focused with my work. Programming and designing algorithms takes a solid amount of focus.

But, I feel much more forgetful. My memory feels like shit now as opposed to previous years. I'll forget things like a coffee mug before heading out. I'll wander into 1 room with the intention of grabbing item x, but grab item y instead and forget about x. I really feel less concious of my environment. Less observant than before. I don't feel like I'm paying attention to the details.

Some factors to take into account. I get exercise frequently. I sleep 6+ hours a night. I drink water and coffee. I'm low carbing and dieting, eating around 1500 calories daily.

Have any of you experienced something similar? So what is causing this mental degredation? How can I reverse this process?