GetProcAddress fails for a function exported with dllexport

Question

First of all, I am new to hooking methods and dll manipulation. I have an assignment to first create a simple program that opens a message box using MessageBoxA. The Code:

#include <windows.h>
#include <iostream>
#include <string>
using namespace std;

int main() {
    LPCSTR text = "Hello World!";
    LPCSTR caption = "My Message Box";
    MessageBoxA(NULL, text, caption, MB_OK);
    return 0;
}

Afterwards, I need to create a DLL that hooks to the program above and opens a different message box. The code I wrote is:

#include "stdafx.h"
#include <windows.h>
#define SIZE 6

typedef int (WINAPI* pMessageBox)(HWND, LPCSTR, LPCSTR, UINT);              //MessageBox function pointer
int WINAPI newMessageBoxA(HWND, LPCSTR, LPCSTR, UINT);            // my detour
void redirect(LPVOID);

pMessageBox pOrigAddress = NULL;
DWORD oldProtect, newProtect = PAGE_EXECUTE_READWRITE;
BYTE origBytes[SIZE];
BYTE jmp[SIZE];

void __declspec(dllexport) myMessageBox() {
    pOrigAddress = (pMessageBox)GetProcAddress(GetModuleHandleA("user32.dll"), "MessageBoxA");      //get MessageBoxA address
    if (pOrigAddress != NULL) {
        redirect(newMessageBoxA);
    }
}
/* Detour */
void redirect(LPVOID newFunc) {
    BYTE tmpJmp[SIZE] = { 0xE9, 0x90, 0x90,  0x90,  0x90, 0xC3 };               //initiate hook (0xE9 = jmp, 0xC3 = ret, 0x90 = nop)
    memcpy(jmp, tmpJmp, SIZE);
    DWORD jmpSize = (DWORD)newFunc - (DWORD)pOrigAddress - 5;                   //jump distance
    VirtualProtect(pOrigAddress, SIZE, PAGE_EXECUTE_READWRITE, &oldProtect);    //change protection to read-write and save previous protection value
    memcpy(origBytes, pOrigAddress, SIZE);                                      //save original value of function address
    memcpy(&jmp[1], &jmpSize, 4);                                               //fill the nops in tmpJmp with the address of the new function
    memcpy(pOrigAddress, jmp, SIZE);                                            //replace jump instruction of old function with new function
    VirtualProtect(pOrigAddress, SIZE, oldProtect, NULL);                       //reset protection value
}

int WINAPI newMessageBoxA(HWND hWnd, LPCSTR lpText, LPCSTR lpCaption, UINT uiType) {
    VirtualProtect((LPVOID)pOrigAddress, SIZE, newProtect, NULL);                                                               // assign read write protection
    memcpy(pOrigAddress, origBytes, SIZE);                                                                                      // restore backup
    int retValue = MessageBoxA(hWnd, (LPCSTR)"This Message Box has been hijacked!", (LPCSTR)"Message Box Hijacked", uiType);    // get return value of original function
    memcpy(pOrigAddress, jmp, SIZE);                                                                                            // set the jump instruction again
    VirtualProtect((LPVOID)pOrigAddress, SIZE, oldProtect, NULL);                                                               // reset protection
    return retValue;                                                                                                            // return original return value
}

After that I changed the first block of code to load the DLL using LoadLibrary:

#include <windows.h>
#include <iostream>
#include <string>
using namespace std;

typedef void(__stdcall *FNPTR)();

int main() {

    HINSTANCE hInst = LoadLibrary(L"C:\\Users\\yuvalnissan\\Desktop\\Workspaces\\VS Workspace\\morphisecAssignment\\x64\\Debug\\dllinject.dll");

    if (hInst == NULL) {
        cout << "\nCould not load dll" << endl;
        return 0;
    }

    FNPTR function = (FNPTR)GetProcAddress(hInst, "myMessageBox");
    if (function == NULL) {
        cout << "\nCould not locate function in dll" << endl;
        return 0;
    }

    function();

    FreeLibrary(hInst);

    LPCSTR text = "Hello World!";
    LPCSTR caption = "My Message Box";
    MessageBoxA(NULL, text, caption, MB_OK);

    return 0;
}

That DLL seems to load properly, but at the command prompt I get "Could not locate function in dll", indicating that the GetProcAddress() is not working properly.

What am I doing wrong?