To be fair, most forms of body dysmorphia are technically a sort of mental disorder, whether it's feeling like a specific limb is alien or feeling like you're in the wrong-sexed body(second part not established scientific consensus, but iirc the leading idea is that they're caused by the same stuff). Essentially the brain has a 'map' of where everything should be in the body, and if you've got something on the map that you don't have in real life, or vice versa, it really doesn't like it. Usually the easiest/most effective ways of fixing it are surgery to remove the parts that don't match up, actually.
But that doesn't mean that's what you've got, necessarily. If it's not a persistent and regularly occurring issue, it might not be an actual disorder of the typical sort, might be something that gets triggered by your body's reaction to hormones or the like. (A fair portion of LGBTQ stuff is hormones fucking up in one way or another during development; for every older brother a male-sexed person has, the relative risk of being gay is multiplied by 4/3; the theory I heard put forward is that the mother's body becomes allergic to the male hormones involved in gestation, basically, for that portion of the contribution(since there's other factors at work as well, obviously.)) I'd recommend seeing a physician about it if you feel comfortable with it, and/or a psychiatrist, just to work stuff out and see where you're at, but only if you feel safe doing so.