About 1,5 months in new job but feeling like Im too slow learner and just frustrate employer. Its a totally different field from what I did at school and havent done much of current job things in life, but still feels dem bad.
As long as he keeps you don't quit it yourself. Even if it's slowly, you still learn and improve. Be sure they ain't charity and that they will fire you if they ain't satisfied with you. To me looks like you're underestimating yourself way too much.
Good employees that want to learn and show up every day and get better are an investment. Just keep pushing forward and owning up to your mistakes when they happen, and they will. Just learn from them and never make them again.