Great, they are your parents so they should understand if you tell them...but keep in mind I'm a guy so I'm not sure how do daughter/parent things work out.
Since they call you for mere conversation this will make it easier to push off since it's nothing important. "I'm putting it bluntly don't flame me :)" If it were money or other situations it would be something hard to put off.
Good luck...and if it still doesn't work, you can always tell your brother about it, and let him sort of slip it to your parents, like saying "Sis ain't doing that well...she's getting called constantly by people and she can't seem to rest up that well" But TAKE NOTE that this might SET GASOLINE TO THE FIRE, and they might CALL YOU TO ASK WHAT'S WRONG...USE WITH CARE! But I'm sure your parents will get the idea, I mean come on they'd have to be stupid to keep calling you after that. :D