No, it's not in your head.
Animal products take a long time and are hard to digest for humans. They're not good for the body. Dairy products are completely unnatural (milk is meant for babies, not adults, and cow's milk for humans is like putting poison in your body).
The more natural foods you eat, the lighter and healthier you will feel.
If you cut out all the processed crap (including the "fake meats", etc). you will feel even better. Try eating ONLY fruit for breakfast and up till midday, and you'll feel even lighter!