The espresso I drink never contains sugar or milk.

The coca cola zero I drink doesn't contain sugar either.

I cannot stand the highs and lows of sugar. I notice it especially at birthday parties. I mean, its already boring... and them comes up of the sugar rush followed by a low where I start yawning and feeling sleepy. I so not wanna be there anymore at that point.

The general trick though, is dosages. You want to keep it stable when it matters, and at the end of the day wind down. Which means you do not want to drink caffeine drinks anymore in the evening.

For the rest, I can highly recommend mindfulness to help increase focus (but before I started it, I found it super annoying when someone suggested it and then I tried it myself and it didn't work out; so I am following a course on it, for people with autism). Meds can help out as well.