Whats wrong with my legs?

sooo i use to be able to run like a 250 meter sprint at pretty much full speed and ever since this 1000m race i cant run more then 70 meters without drastically slowing down......i feel this sharp fatigue pain in my legs...........i tried running the 100 about 4 days after the 1000m race and i got 14 secs while getting 8.33 secs on the 60m.......i got 13.54 secs 100m last year when i ran and i could have prob gotten somewhere close before the 1000m race.........in that race i gave it my absolute all and i felt like i was going to die afterwards......So whats going on here? how do i get my speed endurance back?