Citrus sacrifice their crop of fruit when they become stressed. Your lemon has be repotted, fertilized and overwatered in a matter of weeks. Three stressful events.
Citrus don't go dormant in spring but, any one of those stresses could kill it. Don't overwater, don't fertilize again until next spring.
Citrus trees do better under watered than overwatered but, its not a good idea to do either.