Hello everyone, I'm new to salesforce and I need solution, any help would be great.
My requirement as- We cannot track history for  opportunity line item, soo i have created a custom object, when opportunity stage is after save change from close won to any, the previous value and new change value show display on custom object's field.
The custom object name is "Adjustment".
please suggest me changes in my code 


trigger trackOppProduct on OpportunityLineItem (after insert,after update) {
    List<Adjustment__c> lstOLIH = new List<Adjustment__c>();
    List<Adjustment__c> lstOLIH1 = new List<Adjustment__c>();
    for (Integer i=0; i < Trigger.new.size(); i++) {        
        if(Trigger.isInsert)
        {
            
            for (OpportunityLineItem objOLI1 : trigger.new){
                Adjustment__c objOLIH1 = new Adjustment__c();            
                objOLIH1.ServiceDate__c = objOLI1.ServiceDate;
                objOLIH1.Discount__c = objOLI1.Discount;
                objOLIH1.Description__c = objOLI1.Description;
                objOLIH1.ListPrice__c = objOLI1.ListPrice;
                objOLIH1.ProductCode__c = objOLI1.ProductCode;
                objOLIH1.Quantity__c = objOLI1.Quantity;
                objOLIH1.UnitPrice__c = objOLI1.UnitPrice;
                objOLIH1.TotalPrice__c = objOLI1.TotalPrice;
                objOLIH1.OpportunityLineItem__c = objOLI1.Id;
                
                lstOLIH1.add(objOLIH1);
            }
            insert lstOLIH1;
        }
        
        else
        {        
            for (OpportunityLineItem objOLI : trigger.old){
                Adjustment__c objOLIH = new Adjustment__c();           
                objOLIH.ServiceDate__c = objOLI.ServiceDate;
                objOLIH.Discount__c = objOLI.Discount;
                objOLIH.Description__c = objOLI.Description;
                objOLIH.ListPrice__c  = objOLI.ListPrice;
                objOLIH.ProductCode__c = objOLI.ProductCode;
                objOLIH.Quantity__c = objOLI.Quantity;
                objOLIH.UnitPrice__c = objOLI.UnitPrice;
                objOLIH.TotalPrice__c = objOLI.TotalPrice;
                objOLIH.OpportunityLineItem__c = objOLI.Id;
                
                lstOLIH.add(objOLIH);
            }
            insert lstOLIH;
        }
    }
}