Have You Ever Felt Worthless?

I've always had so much confidence in the amount of time I've spent with God daily. I guess that means my faith was more in my offering than the one that I was offering to. Because of that feeling, I did poorly last semester because I felt as if Bible-reading, prayer, and worship came before school...and it does, in essence, but God understands the fact that we're students. Now that I'm more focused on school, I have time to offer to God, but not as much as I would like. So, the devil is toying with me about that...basically holding it over my head and making me feel as if I'm not good enough in the eyes of God and that I'll never be good at anything beside reading the Bible and praying, so I may as well stick back to that.