Mom giving me a hard time about buying me something?

my mother went with me yesterday to buy a suit for a scholarship banquet with me. It ended up costing around 250-300 dollars and now she is always bringing it up, say things like, "i just bought you a 300 dollar suit, etc. It upsets me because i have 2 sisters who recieved a new dress for everything, like home coming and prom. And my mother spends hundreds on those dresses that they wear once. I will wear this suit several times im sure. So why is she always holding it over my head when she spends 10 times that on my two sisters who do not even use their cloths but once. It just seems wrong to me, not to mention i did just get a schoilarship, i thought they would be proud to buy me a suit... what does everyone else think