First of all, you seem to have a lack of understanding in what overtraining refers to. Overtraining doesn't refer to muscles, but systems of the body. The most highly recognized form of overtraining is CNS fatigue, and deals entirely with the nervous system and I can assure you you are NOT overtraining.
Secondly, your split doesn't involve training legs, which is your biggest mistake. Squats and deadlifts place the entire kinetic chain as well as the endocrine system under the greatest amount of stress, resulting in more anabolic hormone production that further stimulates overall hypertrophy throughout the entire body.
If I were you, I'd switch to an upper/lower split.
Mon: Upper, heavy horizontal, light vertical
Tues: Lower, dynamic effort lower body
Thurs: Upper, heavy vertical, light horizontal
Fri: Lower, maximum effort lower body