How long have you held it? Don't fret over short duration movement.
That said, in looking at that one, it does seem to trail well behind the international fund I have in my blend (which is a 401K fund). The fund you have seems to have a
sizable exposure to emerging markets (~14%), and those have been doing badly, which could help explain your lack of performance. A
different international fund from Vanguard (and better rated) only includes developed markets, and it has done better over the recent years (though it also hasn't performed great this year, but that's life). The lack of emerging markets in that fund reduces your risk and volatility, but it could also potentially reduce rewards if emerging markets start showing higher growth, so just keep that in mind.
Here's a snapshot 5 year view to show how they've fared, with yours (VTIAX) in blue and VTMGX in green:
Edit: I also agree with what GhaleonEB says below. You're getting international exposure in your domestic holdings, particularly your large cap. I still include international in my blend, but it's in the low teens as a percentage, not something approaching 20, 30, or even 40%, as is sometimes recommended. But that's me and I'm not you.