Let me guess, OP: You also recovered almost immediately after you crossed the finish line, right? The fact is, you have to be highly *specifically* trained to get all your energy used up in a single race.
You need races, or at least sustained efforts that approach a racelike intensity, say 15-20min high-tempo runs, to get to that point. Jack Daniels's cruise intervals (e.g. 5mins running alternated with 1min recovery) also help with this.
This is where Lydiard's so-called "time trials"--strong, but not all-out, runs over the race distance--were helpful for his athletes, who sometimes lacked the opportunity to get actual races in before an important meet.
But don't worry too much, in any case. As you say, with 2-3 races you'll be back.