You are probably overworking yourself with energy.
Think about it, spells are a way of focusing your energy. If you cast a lot of spells, you are losing a lot of energy. This is called a "burnout". You may also be spending a lot of energy doing other things. Your body is running out of energy and you need to get some more using this technique:
When you eat, visualize psi energy come out of every morsel of food, going down your throat, and getting stored in the tan-tien (your lower back if you are female, and the lower torso if you are male)