Since June, how much bodyweight have you gained?
What, exactly, did you eat yesterday?
If you've been seeing strength progress with 5/3/1, stick with it. It's designed to be done for long periods of time and you've barely been on it three months.
You should see even better progress for your goals if you use something like the "Boring But Big" template or something with more bodybuilder-style accessory work after the heavy lifts. It's actually not that far off from a "regular" bodybuilder routine. Of course, the lifting is just one part. You've got to improve your eating to see any actual muscle gains.
However, I suggest taking a week or two to do a basic bodyweight plan. I recommend it to all younger lifters to make sure their bodies are fully prepped for even more intense lifting.
Three days a week:
Squat 2x15 (No weight, keep both feet flat on the floor.)
Push-up 2x15 (On your toes, go until the chest almost touches the floor.)
Lunge 2x15 (Alternate legs, 1 rep left/1 rep right.)
Neutral-grip pull-up 2x15 (assisted if necessary. Could be substituted with inverted rows.)
Plank 2x15-count (Hold the top part of a push-up, on the toes, arms straight, keep the whole body straight. Count to 15.)
Burpee/squat thrust 2x15
If that entire session is easy and you can handle each set of each exercise with good form, jump right back into the lifting.