<human>: Give me the gist of the text in a nutshell

To start off I am 21 years old, male, and I've been maintaining a 1500 calorie diet since July 15th. My starting weight was ~220 lbs and now I float between 197-199. It's great that I've lost around 20 pounds, but I have been increasingly growing more and more lethargic. I would say I normally ate 2500-3000 calories/day around two months ago.

I'm a rather sedentary person and I have been for most of life, but the magnitude of my laziness and lethargy has dramatically increased and my procrastination is also increasing. This is something I really can't afford to have in my life right now. It was semi-manageable when I started my diet, but I have just started a new school semester and there is no room for laziness when I'm trying to balance a third year of Biology with Lab and Organic Chemistry. 

I don't really watch anything other than pure calories, but my diet consists of: Chicken, Salmon, Lean Ham, Turkey, Cheese, Wheat Bread, Soup, Cereal, Oatmeal, Soymilk, Coffee, Water.

I've been told by one of my friends who is a fitness nut that my lack of physical activity could be making me feel this way.

Basically my main concerns are my diet has been the same for some time now, but why do I feel so much more lethargic now? Will incorporating some amount of exercise give me a motivational boost?
<bot>: Have been a lazy person most of my life, but laziness and lethargy have exponentially increased recently even though my diet has been relatively the same.