The few times I've taken L-Phenylalanine, I noticed a energy rush similar to caffeine but it only lasts for 30 min tops.
That makes sense since L-Phenylanine is a precursor to tyrosine and eventually turns into dopamine, norepinephine, and epinephrine. Caffeine also boosts dopamine, norepinephrine, and epinephrine. The trouble with caffeine is that after boosting catecholamine levels (catecholamines = dopamine, norepinephrine, and epinephrine) you'll eventually crash. And the bigger the high, the bigger the crash. And you might not even realize your neg feelings are the result of caffeine crash. But L-Phenylanine shouldn't cause a crash.
I'm surprised you got results from this stuff. Based on my experience and reading, I was under the impression that amino acids only help people who have a diet deficient in animal protein or are taking medications/stimulants that deplete them of certain amino acids.