Hello and welcome to MAB.
When I started, a few years back, I lost a fair amount of weight from just becoming active. I didn't track (not that I even knew how) calories either. In addition, I remember how bad my diet would get when weekends came...junk food galore...and I still lost weight. I think that initial weight loss phase is just our bodies adjusting to increased activity. There is no way I could get away with it now.
From the stats you posted of yourself, I think you were WAAAY under for calories...
"Generally little or no breakfast. Lunch is fast food, small qty, but still fast food. Dinner will be soup, or some deli meat sandwich, or chilli. Maybe twice a month pizza." Even this would probably amount to maybe 1500 calories (probably less). Such calorie restriction would work in the beginning, but over time (as I feel has happened to you), your metabolism will stall.
As BTB said, set your calorie intake higher (eg: 2500), avoid processed food (especiallly processed carbs), healthy fats (fish, nuts, avocado, coconut oil, evoo), LOTS of veggies, some fruit, and PROTEIN.
I think counting/tracking calories and your macros is important to ensure fat loss while maintaining, and in your case, probably gaining muscle. If you don't know how, there are many people here that can help you. I have been doing a slow body recomp for the last 2.5 months. The first month was no weight loss, but I was regularily hitting PR's (and felt/looked a little leaner). I wasn't accurately tracking calories though. So I readjusted my tracking and have made progress in weight loss, body measurements, and bf%, while also maintaining strength levels.
You can do it man!! You are in a great place and seem to have a great attitude to reach your goals. Put it to work and I'm sure your "newbie gains" will be making people jealous!!!