How to optimize database connections

Question

In my Go application I use crontab package to run Tracker function every minute. As you can notice from the code I call PostgreSQL function. To interact with the PostgreSQL database, I use the gorm package. Application worked several days without any problem but now I notice an error in logs: pq: sorry, too many clients already. I know that same questions was asked several times in StackOverflow before. For example in this post people advice to use Exec or Scan methods. In my case as you can see I use Exec method but anyway I have error. As far as I understand, each database request makes a separate connection and does not close it. I can't figure out what I'm doing wrong.

main.go:

package main

import (
    "github.com/mileusna/crontab"
)

func main()  {
    database.ConnectPostgreSQL()
    defer database.DisconnectPostgreSQL()

    err = crontab.New().AddJob("* * * * *", controllers.Tracker); if err != nil {
        utils.Logger().Fatal(err)
        return
    }
}

tracker.go:

package controllers

import (
    "questionnaire/database"
    "time"
)

var Tracker = func() {
    err := database.DBGORM.Exec("CALL tracker($1)", time.Now().Format("2006-01-02 15:04:05")).Error; if err != nil {
        utils.Logger().Println(err)  // ERROR: pq: sorry, too many clients already
        return
    }
}

PostgreSQL.go:

package database

import (
    "fmt"
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/postgres"
    "github.com/joho/godotenv"
    "questionnaire/utils"
)

var DBGORM *gorm.DB

func ConnectPostgreSQL() {
    err := godotenv.Load(".env")
    if err != nil {
        utils.Logger().Println(err)
        panic(err)
    }

    databaseUser := utils.CheckEnvironmentVariable("PostgreSQL_USER")
    databasePassword := utils.CheckEnvironmentVariable("PostgreSQL_PASSWORD")
    databaseHost := utils.CheckEnvironmentVariable("PostgreSQL_HOST")
    databaseName := utils.CheckEnvironmentVariable("PostgreSQL_DATABASE_NAME")

    databaseURL:= fmt.Sprintf("host=%s user=%s dbname=%s password=%s sslmode=disable", databaseHost, databaseUser, databaseName, databasePassword)

    DBGORM, err = gorm.Open("postgres", databaseURL)
    if err != nil {
        utils.Logger().Println(err)
        panic(err)
    }

    err = DBGORM.DB().Ping()
    if err != nil {
        utils.Logger().Println(err)
        panic(err)
    }

    DBGORM.LogMode(true)
}

func DisconnectPostgreSQL() error {
    return DBGORM.Close()
}