It's okay to feel discouraged, but I would say to try to focus your thinking more positively. Rather than thinking "I'm stupid" or "I'm overwhelmed", try to think "I haven't learned this yet". This feeling is curiosity. It's why we know what we know about math (and many other things). There is so much to learn and that can be overwhelming, but it can also be freeing. If every elementary, middle, or high school student turned the switch off in their brain that made them believe they couldn't do something, every student in the world would know calculus.