Should I quit my job?

I want start by saying I’m sorry if this is long but I just really need advice. I work for a dollar general and have for 6 months. I get paid $7.25 an hour and I’m honestly miserable. DG is my second job. My first job is also part time because it’s a work study at the college I attend. I don’t need the job. My first job pays more and my fiancée has a nice stable job, but I do like the little extra money it gives. However..there’s a lot I don’t like. My manager was great when I first started. I never had a problem until around January. She became very demanding and angry all the time. She started punishing and reprimanding me for things she had told me was ok to do in the past. She’s very hypocritical. She complains when we use our phones to check the time but she posts on Facebook while at work. She complains if I buy a snack to eat while on the clock yet she and all my other coworkers (except one) go on 10-15 min smoke breaks constantly. I also have a coworker I’ll call M. M is older than me (she’s in her 30s and I’m 21) and honestly she makes my life hell. She is a snitch to put it simply. ANYTHING I do she has to know about it and tell everyone. It started when she started telling my coworkers I don’t straighten the shelves good enough. Then one day I was checking a customer out and she told my other coworker I needed to be working harder. Twice she has pushed me off MY register because “I wasn’t scanning fast enough and I can just bag” Every-time I work and we get our truck and I have to stock (because we have to somehow manage checking customers out, stocking, and cleaning at the same time) she shows up to the store pretending to buy stuff and follows me around the store telling me to make sure to do this and that. It’s very distracting and annoying. She only buys a snack cake or lets her kid buy a toy so I know she doesn’t have to come for something important. Keep in mind she isn’t even the assistant manager. The only difference in our jobs is she is full time and I’m part time. She does stuff like this all the time and is just plain rude to me so I told my manager and she brushed it off. This job just seems to be more trouble than it’s worth. I just don’t know what to do. I know if I quit they will make my last two weeks he’ll but I honestly can’t stand it. It’s emotionally and psychically draining. Please share any suggestions or your stories below. Thanks for letting me rant 😢