No, you don't need to weigh every single ounce of food you put in your mouth. For example, fibrous vegetables (green, leafy vegetables, or vegetables like broccoli) contain very few calories and you can be fine without weighing and measuring them. If you're just starting out, I recommend weighing and measuring most (if not all) foods just so that you can get an understanding of true portion sizes and the energy/macronutrient content of various foods. As time goes on, you will get better and better at estimating portions without weighing and measuring. Constantly weighing all foods is not a sustainable or healthy practice over a long period of time. Rather, it's something to help you get yourself on target and establish consistency. The goal is self-monitoring, not self-obsession.