Why would i feel this way after lifting?

I have noticed that when i steadily start a workout where i am lifting 4 days a week (all different muscles) that i start to get cankers and semi sick towards the end of the week. I eat pretty healthy, don't drink or smoke. drink plenty of water and protein shake after every workout. Why would this be? I will stop when i get this way for a week or two symptoms go away but as soon as i start again i feel the same way.