Hello and welcome to Android Forums ameyadh!

You do not say whether these, "messages", received by your friends are duplicates of those you have previously sent them, or not.

If they are duplicates that are being received, then it is a strong possibility that the fault lies with your carriers messaging service forwarding previously received messages.

On some phones there is also the possibility that some texts can be resent after re-booting. I use the Handcent app, free from the Play Store, for messaging as, among other things, it has a setting to prevent this happening.