ADHD, or just retarted

Im playing MD since Day 1 or so, I’m level 37 but I never made it over Diamond 3. I play Branded and before DM, tried some Decks here and there but I don’t like them. Well, I’m thinking about quitting, it’s actually only grinding and I don’t want spend money (don’t even if it will help I have most cards and all essentials (Maxx C, Ashes etc.) Don’t know what I’m doing wrong or is it too much of a goal to get over Diamond?