I am also 19, and also feel like a failure sometimes! School is really hard, and I realized that it's mostly because I have ADHD and went undiagnosed for most of my life lol. I hate the idea that people our age must be going to school and doing well, otherwise they are a failure. Being our age means that we are meant to fail until we figure out what works for us. Some people don't do well in college! That's okay! Trade school is a wonderful alternative, and there are plenty of online certificates to get for other jobs, like fixing computers (which I once looked into because of my own struggles)!
My solution, before I realized I had ADHD, has been to take community college classes (because they are cheaper) and working to save up money. I take whatever amount of classes I can handle in a semester and try not to stress myself while I figure out what I want to do with life. I know that you may feel like a failure, but I assure you that there are so many people our age who feel the same way you do. We just don't talk about it because we feel ashamed lol.
Also, no offense, but your mom sucks. Do you have any other people you can stay with, or is this your only/best option for now? I realized that my high school living situation was a big stressor in my life, so as soon as I turned 18 I moved in with another family member who was willing to take me in. It completely changed things for me! If you can't, maybe try to find a community of people who will support you to offset your mom's comments; like a hobby group or something!
And, regarding the replies suggesting Adderall as a study aid: I do not think you should be taking Adderall unless you are prescribed it for ADHD. Slippery slope. Even I have been very careful with it, despite having a prescription. It would be stupid to use it, especially if you are struggling mentally because the feelings that come with taking it can be addictive. I almost had a moment where I wanted to take more than I needed because of how it made me feel, but it is in no way worth it. Withdrawal sucks.