Based on the problem solving skills demonstrated in your attempt to help yourself learn better, you're definitely not dumb. I second the note about getting tes

Based on the problem solving skills demonstrated in your attempt to help yourself learn better, you're definitely not dumb. I second the note about getting tested for ADHD. Another reason could simply be performance anxiety or imposter syndrome. Have you tried joining a study group ? If you can find a positive group of people to study with, you might feel less anxious about it. Perhaps also consider talking to your professors. It sounds like you're trying and they always want to help.