It is normal, but only if you are using your energy in a very inefficient way. The reason people use spells and rituals is to focus energy more efficiently. Some people don't have the ability to focus energy without them enough to accomplish anything. If you are finding yourself exhausted after using magic, try using a spell or a ritual to accomplish what you are wanting to do, instead of the think-do magic. See if you are less exhausted afterward. Either that or try to focus on using the bare minimum possible amount of energy to get the job done. Both techniques will help you retain your energy and not spend all of it at once.
You can also just recharge your energy when you're done. If you don't want to be bothered trying to find a more efficient way to work magic, see about finding a source to recharge from. Be warned however that not all sources work for all people. If you are drawing energy from a particular source and you start feeling funny, try a different source.