How do I know if I'm training correctly?

I was forced to take a break due to illness, but I've been training regularly for three months now. For the first two months I focused more on cardio because I needed to lose a bit of weight first. Now I'm at the point where I want to lose another 2-3 kilos, but very slowly to keep the weight off. I train to muscle failure as often as possible, and I like to take my time on the weekends, but I sometimes come out of training and am still totally fit, which kind of annoys me. Plus, I'm only seeing slow progress, which is completely legitimate because it's not my goal to become a bodybuilder. I'm just "afraid" of training badly, doing something wrong, not really giving 100%. How did it go for you? I should also briefly mention nutrition: I don't track calories; I do it roughly in my head because tracking drives me crazy, but I'm still slightly in deficit (I estimate 100-200 calories, sometimes more, sometimes less). I try to eat protein as best I can, but I'm not reaching my daily target. I don't take shakes or creatine at all; I just find that stuff disgusting; it's no good for me at all.