three things:
1. You do not enjoy your work, and thus have no motivation.
2. Maybe you should not do the work and suffer the consequences.
3. You have built a mental dependency that you must take amphetamines to "focus", and this hinders your real ability to focus.
All of those things ^^^ I have experienced at one point or another in my life. You can focus, you have to make yourself. There is no other way. You do not need medication... But maybe you do, I highly doubt it though.