Box collider (with Rigidbody attached) gets stuck into another Box Collider

Hi there, I’m having some problems by moving a box collider with a rigidbody attached to it through another Box Collider, just like a Player moving on top of a platform, the problem is that it gets like inside of the platform collider, it’s strange and 'cause of it it slows the Player instead of adding speed, I did search for a solution but I didn’t find anything. There’s an image of what I’m saying:

And there’s my own movement script (still in development):

using UnityEngine;
using System.Collections;

public class PlayerMovement : MonoBehaviour {
    public float normalSpeed;
    public float maxSpeed;
    public float jumpForce;

    public bool isOnGround;

        // Use this for initialization
        void Start () {
        
        }
        
        // Update is called once per frame
        void Update () {
        print(rigidbody.velocity.magnitude);
        if (rigidbody.velocity.magnitude > maxSpeed)
        {
            rigidbody.velocity = rigidbody.velocity.normalized * maxSpeed;
        }
        if (Input.GetKey("left"))
        {
            rigidbody.AddForce(-normalSpeed, 0, 0);
        }
        else if (Input.GetKey("right"))
        {
            rigidbody.AddForce(normalSpeed, 0, 0);
        }
        if (Input.GetKeyDown("up"))
        {
            if (isOnGround == true)
            {
                rigidbody.AddForce(new Vector3(0, jumpForce, 0), ForceMode.Impulse);
                isOnGround = false;
            }
        }
        
        }

    void OnCollisionEnter(Collision collision)
    {
        if (collision.collider.tag == "ground")
        {
            isOnGround = true;
        }
    }
}

I’ll be looking for answers, and possibly a solution. Thankyu.

Help, please!