2D A* Pathfinding Enemy AI

So I'm making a top down zombie game in Unity using the A* navigation tools. I'm trying to get my zombies to look at the direction in which they are going. I got something that sort of works, but it won't turn a certain way whenever it gets closer to the target, and on top of that when it's moving it sort of "twitches".

Here's the code

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using Pathfinding;
4.  
5. [RequireComponent (typeof (Rigidbody2D))]
6. [RequireComponent (typeof (Seeker))]
7. public class EnemyAI : MonoBehaviour {
8.  
9.     // What to chase?
10.     public Transform target;
11.    
12.     // How many times each second we will update our path
13.     public float updateRate = 2f;
14.    
15.     // Caching
16.     private Seeker seeker;
17.     private Rigidbody2D rb;
18.    
19.     //The calculated path
20.     public Path path;
21.    
22.     //The AI's speed per second
23.     public float speed = 300f;
24.     public ForceMode2D fMode;
25.    
26.     [HideInInspector]
27.     public bool pathIsEnded = false;
28.    
29.     // The max distance from the AI to a waypoint for it to continue to the next waypoint
30.     public float nextWaypointDistance = 3;
31.    
32.     // The waypoint we are currently moving towards
33.     private int currentWaypoint = 0;
34.  
35.     private bool searchingForPlayer = false;
36.    
37.     void Start () {
38.         seeker = GetComponent<Seeker>();
39.         rb = GetComponent<Rigidbody2D>();
40.        
41.         if (target == null) {
42.             if (!searchingForPlayer) {
43.                 searchingForPlayer = true;
44.                 StartCoroutine(SearchForPlayer());
45.             }
46.         }
47.        
48.         // Start a new path to the target position, return the result to the OnPathComplete method
49.         seeker.StartPath (transform.position, target.position, OnPathComplete);
50.        
51.         StartCoroutine (UpdatePath ());
52.     }
53.  
54.     IEnumerator SearchForPlayer()
55.     {
56.         GameObject sResult = GameObject.FindGameObjectWithTag("Player");
57.         if (sResult == null)
58.         {
59.             yield return new WaitForSeconds(0.5f);
60.             StartCoroutine(SearchForPlayer());
61.         }
62.         else {
63.             searchingForPlayer = false;
64.             target = sResult.transform;
65.  
66.             return false;
67.         }
68.  
69.     }
70.    
71.     IEnumerator UpdatePath () {
72.         if (target == null) {
73.             //TODO: Insert a player search here.
74.             return false;
75.         }
76.        
77.         // Start a new path to the target position, return the result to the OnPathComplete method
78.         seeker.StartPath (transform.position, target.position, OnPathComplete);
79.        
80.         yield return new WaitForSeconds ( 1f/updateRate );
81.         StartCoroutine (UpdatePath());
82.     }
83.    
84.     public void OnPathComplete (Path p) {
85.         Debug.Log ("Path found. Error?" + p.error);
86.         if (!p.error) {
87.             path = p;
88.             currentWaypoint = 0;
89.         }
90.     }
91.    
92.     void FixedUpdate () {
93.         if (target == null) {
94.             //TODO: Insert a player search here.
95.             return;
96.         }
97.        
98.         //TODO: Always look at player?
99.        
100.         if (path == null)
101.             return;
102.        
103.         if (currentWaypoint >= path.vectorPath.Count) {
104.             if (pathIsEnded)
105.                 return;
106.            
107.             Debug.Log ("End of path reached.");
108.             pathIsEnded = true;
109.             return;
110.         }
111.         pathIsEnded = false;
112.    
113.         //Direction to the next waypoint
114.         Vector3 dir = ( path.vectorPath[currentWaypoint] - transform.position ).normalized;
115.         dir *= speed * Time.fixedDeltaTime;
116.        
117.         //Move the AI
118.         rb.AddForce (dir, fMode);
119.  
120.         if (target != null) {
121.             Vector2 dir = WorldPos - transform.position;
122.             float angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
123.             transform.rotation = Quaternion.AngleAxis(angle, Vector3.forward);
124.         }
125.  
126.         float dist = Vector3.Distance (transform.position, path.vectorPath[currentWaypoint]);
127.         if (dist < nextWaypointDistance) {
128.             currentWaypoint++;
129.             return;
130.         }      
131.     }
132. }
133.  

Can somebody tell me why this is? Or better yet a more effective / better way to make this happen?

Thanks,
James