Why do i get worse in singing when i practice more?

I'm a very good singer naturally and I figured that I want to make it my life. But it seems that when I really start to put a lot to practice in it and get serious, I feel like i'm starting to get worse. Ya I have some days that I sing better then others but it seems the more i practice the worse i get. and its not that im overdoing my voice, its just the singing. can anyone answer this?