Yes, it is absolutely fine for you to use your time off. If your employer balks at you for this, then you do not want to work for them.
However, you still need to get the exact timing approved by your manager. Before you go to them, think about your responsibilities. Will the time off cause you to miss any deadlines you've committed to meet? Are you responsible for any tasks that will need to be performed while you're gone? If so, find a solution if at all possible.
If you say to your supervisor "I'd like to take the last week of January off. This will not affect my ability to meet my deadline on Project X, and Sally said she will run my weekly reports for me while I'm gone. Is it okay for me to take that week off?", then they will likely respond with, "Enjoy your vacation!" Show that you've been thoughtful about the impact of your absence, and you will be seen as a team player that cares about the company.
If there is a lot going on that particular week and you being gone then will cause problems that aren't easily solved, then they may ask you to take a different week off instead. This is reasonable, especially if you're giving them short notice. You absolutely should insist that you get to take the time off that you're entitled to, though, even if you don't get to take it exactly when you want to.