Comment by KohgnaK

Lots of great answers, thanks to all of you!

The solution of my problem probably lies in the mix of most of your answers; what I'm thinking about doing is:

1. Start waking up earlier in the morning and power nap to counterbalance any sleepiness in the afternoon

2. Be more strict in terms of diet, eat real food + no more coffee after lunchtime

3. Stop working overtime (weekend notably), to try to reduce the procastrination on small tasks

4. Talk with management and try to find some possible arrangements (maybe get a minion?)

5. Find a position where I would have only one major job, not 3 or 4.

Cheers!