If you've just started, that means you're probably taking survey courses, which are not meant to be specific. These courses are where you can start figuring out what particular aspects of history most interest you (or determine that maybe it doesn't really interest you as much as you thought). Depending on your institution, history majors have certain requirements they have to meet in order to graduate with a bachelor's degree in history. For example, for my undergraduate degree, I had to take classes from: (1) at least five different geographic areas; (2) at least 3 time periods; (3) 2 historiography courses; (4) 18 hours of upper level history courses; (5) a capstone project on a topic of my choice.

As you progress through your degree program, the classes (moving from Freshman level courses to Junior/Senior level) should get more geographically and chronologically specific, which should allow you to focus on the area you're most interested in.

Make sure you are signing up for those classes that are most related to your subject interest - undergraduates oftentimes don't really get a choice so you have to make it work. Many history departments will accept history classes from other departments. So, if the Classics department offers a course in literature of the Roman Republic, that may also count for an "ancient history" credit for your degree. If the English department offers a class on Old English poetry, that may count for a "European history" credit. Make sure you talk to your department advisor about something like this.

Many undergraduate degrees are only meant to dip your toes into the world of academic history simply because the students do not yet have the knowledge, experience, or research skills necessary for super-specific courses. If you plan on continuing to graduate studies, that is where you will really get into the meat of academic history, having established good fundamentals at the undergraduate level. Talk to your professors, and establish a good report, because they will be the ones writing your letters of rec. for grad school, and may have contacts that will help get you a spot (this is how many grad. students get into programs).

I will give you one piece of advice. If you're going to study Vikings or Rome, and you don't already know Latin, you need to take as many Latin classes as you can. Minor or double major in Latin even. You cannot be a Roman or medieval historian without knowing Latin. I would also suggest picking up another European language (especially French or German) if you don't have a handle on one of those, too. Feel free to PM with any more specific questions you have, but your best course of action is to ask you history professors, because they've gone through the same set of circumstances you're going through now.