Eh, you were probably experiencing the effects of improper dosing (as well as - I'm assuming - different means of ingestion).
Methamphetamine is just amphetamine with an additional methyl group, which makes it cross the blood-brain barrier more easily, and means that a lower dosage by weight is necessary for the same outcome.
Methamphetamine is metabolized almost identically to amphetamine, which means that the pharmacokinetic impact is the same.
The main difference is that methamphetamine is generally smoked (or occasionally snorted and injected), whereas amphetamine is prescribed orally. Also, unless you were prescribed Desoxyn, there's the other question of how pure and reliable the methamphetamine is, and what other compounds were present.