DMG page 141 (and the corresponding section of the basic rules) states:
Multiple Items of the Same Kind
Use common sense to determine whether more than one of a given kind of magic item can be worn. A character can't normally wear more than one pair of footwear, one pair of gloves or gauntlets, one pair of bracers, one suit of armor, one item of head wear, and one cloak. You can make exceptions; a character might be able to wear a circlet under a helmet, for example, or be able to layer two cloaks.
Belts aren't specifically mentioned here, hence you will have to ask your DM if it's possible.
I personally would say no; wearing two belts would be about as practical as wearing two cloaks, which is generally disallowed (unlike wearing multiple rings, for example, which shouldn't be an issue).
Yet, under some circumstances, you might be able to layer two cloaks - but that's up to your DM to decide, and the same thing goes for belts.
Other than the limitations on attuned items, and common sense, there is no reason you cannot wear two belts. It is frequently done for stylistic purposes. Two cloaks is also not specifically prohibited, or necklaces, or rings. If they can fit, they can be worn, always under teh authority of rule 0. I myself have several cosplay costumes employing multiple cloaks and belts. It is a common trope amongst fantasy characters to do this sort of thing. Lulu, from final fantasy x comes to mind specifically. As DM, i would allow this.