You should definitely look into organizing a proper training program as well as reading up on various "clean bulking" plans. I usually try to set my calories 200-300 over my maintenance while clean bulking and I eat fairly well, things like oats, brown rice, chicken breast, eggs, and various fruits and vegetables.
As for the workout, research shows that light weight for lots of reps builds about the same amount of muscle as heavier weights, it's just lacking the strength gains.
I personally do a mixture of light and heavy bodyweight exercises alternating every second day, so Day 1 heavy, Day 2 rest, Day 3 light, Day 4 rest, etc
As for bodyweight variation, here's some examples:
Light: regular pushups for 20-30 reps
Heavy: pseudo-planche pushups for 3-5 reps
Light: stepping lunges for 30-40 reps
Heavy: pistol squats for 3-5 reps