Feeling unappreciated at work

I d don't know what group to post this on, but I'm so fed up with my job it's unreal. I've been at my store for 3 years, longer than my own manager. And I've never felt more unappreciated in my life. I was suppsed to learn paperwork to be assistant manager becasue my manager is pregnant and due in November, well every person we hired wouldn't stay longer than a week. So we put it on hold. While I was on my vacation in July they hired my cousin, and all the sudden she's learning paperwork and no one tells me anything. But it's like I'm in the wrong becuase I was waiting for my manager to tell me when to learn it, and that I didn't show initiatve to learn the paperwork. So now I'm SOL and my cousin hasn't even worked here 90 days yet, and my seniority don't matter. They even said they wouldn't be suprised if I moved to a different store that didn't have a deli. I just feel like I'm an outcast. This is the 3rd time I've been overlooked, or passed up. 😔 so I'm becoming depressed