I delivered 4 months back. It was a vaginal delivery. How soon before I can resume having sex?

It differs for everyone - how they are healing, how they are feeling. There is no set time and the most important thing is to wait until you are ready - physically and emotionally. Some couples have sex after the bleeding stops, a little after one month post birth, some wait until at least 6 weeks if they had an episiotomy. Most couples wait till after 3 months and some couples prefer to wait until after 6 months.