are cloths getting smaller or am i getting bigger?

ok so here is my delema. i have always been a big girl ive never been small. ive been the same size for the last two years ive always worn a size 22 and ive gotten taller but i did gain a tiny bit of weight but i still fit all my cloths fine. so ive been wearing my same basic wardrobe but i had plans to dinner last night with my family to go to a fancy restuarunt for my sisters birthday. i went shopping with my mom and NONE of the cloths fit me so i tired on 24 and 26 sized jeans and even they didnt feet but i know darn well i dont wear a 26 because all of my cloths are 22!! and 2X and 3X shirts. most of the cloths i own ive had for over a year though so i wanted something new. so i came home upset crying because im fat and gaining weight but the pants i wore to dinner are a 21/22!! and the jeans im wearing now are also 21/22 so i really dont understand. am i just getting really fat or are cloths just getting really small. all the jeans in my wardrobe are 22 and maybe one size 24 for that time of the month. i know i couldnt possibly wear a 22 one minute then a 28 next??? im lost and upset that i cant go shopping, i went to three different stores and couldnt find anything. also does anyone know any online plus sized stores that arent over the top expensive i can shop at, im going to need new pant eventually haha.