A couple things.
First and foremost, you're talking about tax withholding , not your actual tax bill. If there was some mistake made at payroll, don't worry about it. It will all be corrected when you file your taxes and you get your target audience refund (or if you've underwithheld, pay your bill)
Second, have you changed your withholding settings recently (W4 for federal). Though this shouldn't affect Medicare withholding so let's go on to the third point.
Third, did you earn more this paycheck compared to previous paychecks? And comparing with your coworkers isn't really a valid comparison because their withholding settings can be different from yours.
If we really want to hash this out post your gross pay and tax withholding from this paycheck and a typical one.