platform generation for endless runner using object pooling

Hello everyone, I have been working on my own to make an endless 2D runner. I am kind of stuck in platform generation, where I want to generate platform in three levels i.e Bottom, mid and top. Right now I am able to generate platforms at the bottom at a Random position, but when I generate platforms at mid and top, game kind of lags.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;

 [System.Serializable]
 public class ObjectPoolItem
 {

 public GameObject objectToPool;
 public int amountToPool;
 public bool shouldExpand = true;

 public ObjectPoolItem(GameObject obj, int amt, bool exp = true)
 {
     objectToPool = obj;
     amountToPool = Mathf.Max(amt,2);
     shouldExpand = exp;
 }
 }

 public class ObjectPooler : MonoBehaviour
 {
 public static ObjectPooler SharedInstance;
 public List<ObjectPoolItem> itemsToPool;


 public List<List<GameObject>> pooledObjectsList;
 public List<GameObject> pooledObjects;
 private List<int> positions;

 void Awake()
 {

     SharedInstance = this;

     pooledObjectsList = new List<List<GameObject>>();
     pooledObjects = new List<GameObject>();
     positions = new List<int>();


     for (int i = 0; i < itemsToPool.Count; i++)
     {
         ObjectPoolItemToPooledObject(i);
     }

 }


 public GameObject GetPooledObject(int index)
 {

     int curSize = pooledObjectsList[index].Count;
     for (int i = positions[index] + 1; i < positions[index] + pooledObjectsList[index].Count; i++)
     {

         if (!pooledObjectsList[index][i % curSize].activeInHierarchy)
         {
             positions[index] = i % curSize;
             return pooledObjectsList[index][i % curSize];
         }
     }

     if (itemsToPool[index].shouldExpand)
     {

         GameObject obj = (GameObject)Instantiate(itemsToPool[index].objectToPool);
         obj.SetActive(false);
         obj.transform.parent = this.transform;
         pooledObjectsList[index].Add(obj);
         return obj;

     }
     return null;
 }

 public List<GameObject> GetAllPooledObjects(int index)
 {
     return pooledObjectsList[index];
 }


 public int AddObject(GameObject GO, int amt = 3, bool exp = true)
 {
     ObjectPoolItem item = new ObjectPoolItem(GO, amt, exp);
     int currLen = itemsToPool.Count;
     itemsToPool.Add(item);
     ObjectPoolItemToPooledObject(currLen);
     return currLen;
 }


 void ObjectPoolItemToPooledObject(int index)
 {
     ObjectPoolItem item = itemsToPool[index];

     pooledObjects = new List<GameObject>();
     for (int i = 0; i < item.amountToPool; i++)
     {
         GameObject obj = (GameObject)Instantiate(item.objectToPool);
         obj.SetActive(false);
         obj.transform.parent = this.transform;
         pooledObjects.Add(obj);
     }
     pooledObjectsList.Add(pooledObjects);
     positions.Add(0);

 }
 }

The above is code for ObjectPooling. and below is my logic for platform generation, right now it is generating platform only at bottom level.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;

 public class Spawn : MonoBehaviour {

 public Transform generationPoint;

 private float distanceBetween;
 public float distanceBetweenMin;
 public float distanceBetweenMax;

 private float width;
 ObjectPooler objectPool;

 void Start()
 {
     objectPool = ObjectPooler.SharedInstance;
     
 }

 void Update()
 {
     if (transform.position.x < generationPoint.position.x)
     {

         distanceBetween = Random.Range(distanceBetweenMin, distanceBetweenMax);
         int index = Random.Range(0, 3);
         width = objectPool.GetPooledObject(index).GetComponent<BoxCollider2D>().size.x;
         transform.position = new Vector3(transform.position.x + (width / 2) + distanceBetween, transform.position.y, transform.position.z);


         GameObject newPlatform = objectPool.GetPooledObject(index);
         newPlatform.transform.position = transform.position;
         newPlatform.transform.rotation = transform.rotation;
         newPlatform.SetActive(true);

         transform.position = new Vector3(transform.position.x + (width / 2), transform.position.y, transform.position.z);
     }
 }
 }

[1]: /storage/temp/121546-untitled.png

This is the way how I want to generate platforms, i.e whenever there is a gap between the two bottom level platform a mid-level platform is generated at some height to fill this Gap.

All the help is appreciated and i new to unity. :)