So I started going back to the gym after taking some time off due to a back injury.
It seems that when I go and train with weights, I feel like crap afterwards (not tired/sore but my frame of mind is bad). However, if I just do dips, various pull-ups/chin-ups, and the ab wheel followed by 30 minutes on a machine I feel awesome.
Before, I would feel good after training with weights but not now.
Definitely diet is an issue. For six years I laid off lifting, feeling the same way as you did- less fatigued from bwe, total gym,isometrics, etc. Start lifting with light weights, easing into it. Train each body part once per week, clean up your diet, supplements are a must if you are older-protein, aminos, fish oil, a multi, and maybe a test booster.
If you can do bwe then you can do weights. The key, at least for me is that once per week per part. Cardio is a must but don’t go crazy with that either. I don’t think lifting is the problem as much as the overdoing it. Growing up in the 60’s and the Arnold era I thought that 6 workouts per week was the way to do it. Wrong. Experiment and find what works for you.