My baby is 2 months old and healthy , is it necessary for him to have regular check ups with a pediatrician, if so , how frequent?

Depends: If your kid is worthy of the standard care of today s/he will see a doc every 2 months until 6 mo, then every 3 mo until 18 mo. At many of those visits s/he would get vaccines but at every visit growth and development would be monitored & treatable conditions found. Kids have certainly survived without in past centuries, but many did not.