Quite possibly more than calories, is what those calories are (what is your average calorie count these days?) Since you are already taking B12, that's not likely it (B12 is more of an RNY thing than a VSG thing, but some can be intrinsically low it irrespective, or just diet is low in it for now, though most multivitamins have enough to do the job.) Overly low carbohydrates are frequently a cause of low energy in the absence of other anemia indicators, as that is where our quick energy comes from. It is what helps us chase down that antelope for dinner, or quickly climb a tree to avoid being a lion's dinner (hoping it's not a leopard chasing us!)
We typically burn off our glycogen reserves (basically stored carb, held mostly in the muscle tissues) and the water that keeps it in solution first,, usually in the first couple of weeks or so, and then pause while we start to access our fat reserves to rebuild the glycogen back to a functional level - hence the typical rapid weight loss followed by the "three week stall". You may well still be trying to rebuild your glycogen stores to get you that everyday energy that you are expecting. I have seen some programs that specifically want their patients to do a bit of lightweight "carb loading" after surgery to counter this problem - things like oatmeal, cream of wheat, sloppy mashed potatoes, unsweetened apple sauce, watered down fruit juice, etc.
I never had consistent energy problems as you describe, though I did run out of gas more quickly for a while - afternoon naps in the first 2-3 weeks were common and my bedtime shifted an hour or so earlier (my circadian rhythm has stayed shifted by an hour or so ever since - about an hour earlier to bed and hour earlier to get up,) but even within the first week I was outpacing my wife on our walks (granted, not a real high bar, but still....) I was back at the gym within the first 2-3 weeks, mostly to keep my wife in the habit, I basically just walked on the treadmill or did some gentle bike or elliptical work to explore range of motion, but moderate energy was there. I was up into the 900-1000 calorie range within the first couple of weeks, and the doc was adding more veg to the diet as my protein was satisfactory at 90+. I wasn't specifically carb loading, but neither was I avoiding them - just eating as healthy as possible within the limitations. Later, however, after about four months I was running into an energy wall after about an hour in the pool, and after consulting with the RD on it and added some complex carb ahead of my gym time, I found that a simple piece of toast made all the difference in breaking through that wall. So simple things can make a difference.