The first thing I think asooneyeonig is trying to establish if what are your weights on the major lifts? Squat, bench, deadlift, overhead press. Given that you've been training for 3 years and are only doing 3 -4 sets, you probably stopped making gains about a year ago, maybe longer. After a year to 2 years of serious lifting you would need to increase your volume to continue to make progress whether it be for size or strength. And personally I feel that full body workouts don't build the maximum amount of muscle possible unless you're on AAS/PHs or you're genetically gifted for synthesis. My current split looks like so:
Day 1 - Quads/Calves
Day 2 - Chest/Delts/Tris
Day 3 - Hamstrings/Calves
Day 4 - Lats/Traps/Bis
You can throw in rest days when ever you'd like but I've gone 3 weeks straight on this split multiple times with no signs of overtraining what so ever.