Hi amit1989,
Many Test Takers need time (and heavy practice) to get comfortable with DS. It's a question type that is unique to the GMAT and tests you on a lot of different skills besides "math skills", including organization, accuracy, attention-to-detail, thoroughness, pattern-matching, the ability to prove that you're correct, etc.
Thankfully, the question type is standardized and predictable, so you can train to earn these points. A combination of math knowledge/ability and tactical approaches is required though - and those skills often take time to develop.
What materials have you used so far during your studies to help you practice DS?
GMAT assassins aren't born, they're made,
Rich