What do you expect to do on your vacation? April in Myrtle Beach, we would be out in jeans and windbreakers, sweaters underneath. Canadians would be starting to come down to swim in the ocean, golfers to play.
Further inland on the coastal plain, sunny days would be warmer than at the coast, cold dank days cooler. Quite changable, feeling like late winter, spring, or early summer, day to day.
I was also in D.C., March and April. Glorious warm sunny days, cold dank reprises of winter, weather systems coming through weekly.
If the Gulf Stream is where it is supposed to be, coastal Virginia, on the peninsula, will consistently have some of the nicest weather north of Charleston at that time of year. It is often more mild in January-March than most places further south. But this is a coastal effect, weather may not be the same inland. And a system blowing cold air off the continent can give you brisk days.
Spring breaks from eastern Pennsylvaniia, through easten Virginia, coastal Carolinas, some have been cold, some cool, some wet, some warm and sunny. It is spring, weather is changeable.
Hope for nice, but no guarantees.