Will the sodium from sports drinks make me retain water?

That depends.
No, if you're worried about excess fluid retention associated with increased blood pressure or body weight. The body very efficiently regulates blood sodium so the small amount in sports drinks (no more than a slice of bread or glass of milk) is insignificant.
Yes, if you consider what happens during exercise. By replacing sodium lost in sweat, it helps maintain extracellular fluid volume and stimulates drinking. This limits dehydration, heat illness and decreased performance.
-- Mark Davis Ph.D., Department of Exercise Science, School of PublicHealth, University of South Carolina