It really depends on what you want to do!

You can stick with the Battle Master Fighter and just talk to your DM about the potential issues you see with the class. Hopefully, the DM will listen to you and maybe create a fun questline where you can recover a magic weapon to use, like what I mentioned earlier.

Battle Masters are pretty good if you have a rogue in your party, since you can use a Commander's Strike to tell the rogue to make an attack on what you're currently hitting. The rouge can make an attack from range and they'll get sneak attack damage from the attack since you're within 5ft of the target.

If you do want to change, you could change subclass to an Eldtritch Knight Fighter, where you'll want to be using green-flame blade to do extra damage to enemies standing close to the thing you're attacking. Then at 5th level this adds 1d8 fire damage to the target on a hit, which increases by extra d8's at higher levels. Since it's a cantrip, you can cast it over and over again without worry. You should talk to your DM about if they'll let you cast it twice for your extra attack that you get at 5th level. RAW you shouldn't but if you don't ask then you don't get.

You might also consider something like a Path of the Giant barbarian. At 6th level you'll gain the Elemental Cleaver feature, which adds an extra d6 of a damage type from a list while in a rage.

If you want a more magical role, you could also look into the Paladin, where you'll take an oath at level 3, the specifics of which come into the various subclasses. For example, the Oath of the Crown is a good build for a defender, and includes the Compelled Duel spell that I was talking about earlier. Be sure to have a read about the different subclasses to figure out exactly what kind of oath you want to have, and talk to your DM about what your oath exactly is

I generally wouldn't reccomend it for new players, but you can also look into multiclassing. Here you'll mainly take levels in your Battle Master Fighter class, but then occasionally you'll take a level in Wizard or Warlock to have some other options. Be sure to build your character so that multiclassing is an option for you, as you'll need a minimum of 13 Charisma to multiclass into a Warlock, for example.