Does anyone else have issues with shampoo?

hear me out, I feel like I buy different shampoo a lot.
  1. I can buy one brand of shampoo and use it for a month or two, then all of a sudden it's like my hair gets used to it. Then it stops working.
  2. Am I the only one?
  3. Am I imagining it?
  4. I don't buy the cheep stuff, but I also don't buy the crazy expensive stuff. I get mid level name brand.