cant do it anymore

So im a neuroscience major and I have two classes im having issues with. I have a D+ in these two classes and I spend hours, and I mean hours, studying for them but I just cant seem to pass any of the tests no matter what I do. I applied for a tutor but tutoring usually doesnt work with me. I just honestly feel so defeated and im thinking about switching my major, even though I really dont want to but its just getting to be too much for me. On top of that I work 40 hours a week to pay for school so that adds to the stress. I just need some words of encouragement, because right now I feel like giving up.