What can I change in my diet to feel better?

Hiya. I’m looking for a diet makeover—not necessarily to lose weight, but rather to feel better. I’d appreciate your input very much.

I’m a generally healthy eater, but lately—and come to think of it, for a while now—I’ve been having some serious gas, and feeling lethargic.

Some considerations: I think that I may be lactose intolerant, at least a little bit; and I also believe that my body doesn’t process fruits and vegetables as well as it could/should. I also believe that the weather, for example when it’s overcast, affects my energy levels. Something feels just… off.

Here’s my general diet:
—Breakfast – oatmeal, eggs, cheese, veggies, sometimes a bagel and cream cheese, lox (I do live in NYC…) :)

—Lunch/dinner: lots of raw veggies, like carrots, cucumbers, tomatoes, avocado w toast and sea salt, chicken (cooked breast on a cast iron w/ spices), spinach, green beans, Brussels, fish (e.g. Trader Joe’s frozen fish), beans, sometimes rice.

—Misc: cashews and almonds, coffee w ½ and ½ in the morning; sometimes some chocolate or candy, but not so often; lots of gum. I also smoke cigarettes sometimes (maybe 2 a day). My exercise is sporadic—either 3 or 4 times/week, or not at all. I’m an average weight, maybe a bit heavy (6 feet, 200 lbs.).

Thoughts? Happy to answer questions.