Hello all

i am trying to Design a Trigger where it should throw an error upon duplicate record creation, i know this can be achived with Duplicate management, but i have Custom Lookup field(User) which is not showing in the matching rules, Hence i am trying to write trigger, basically i have 3 Custom fields User(Assignedto__c ) which is 
Lookup(User) and other fields are 
Quater_Year__c which is picklist and Month (
Month__c) which is picklist field, 

Please Help with the trigger

trigger contactDuplicatePreventer on Contact(before insert, before update) 
{
	Set<String> setEmailID = new set<String>();
	Set<Id> setContID = new set<ID>();
    for (Contact Contact : System.Trigger.new) 
	{
        if ((Contact.Email != null) &&  (System.Trigger.isInsert ||  (Contact.Email != System.Trigger.oldMap.get(Contact.Id).Email))) 
		{
			setEmailID.add(Contact.Email);
			setContID.add(Contact.id);
		}
    }

	List<Contact> lstCOntact = [select id ,email from contact where email in :setEmailID and id not in :setContID ];
    Map<String, Contact> contactMap = new Map<String, Contact>();

	for(Contact cont : lstCOntact)
	{
		contactMap.put(cont.email, cont);
	}	

    for (Contact Contact : System.Trigger.new) 
	{
        if ((Contact.Email != null) &&  (System.Trigger.isInsert ||  (Contact.Email != System.Trigger.oldMap.get(Contact.Id).Email))) 
		{
			if(contactMap.containsKey(Contact.Email))
			{
				Contact.Email.addError('A Contact with this email address already exists.');
			}
		}	
	}	
}