There are several days where I just don't want to do it. Actually, I'd say that it's every day. Sometimes I get dressed and by then I am excited; some times it doesn't happen until I am done with my workout. And just to be clear, I'm speaking as someone who has been doing exercise for years, exercise that I love - once I get going.
It's not always going to be easy, it's not always fun, but you'll find that as you get consistent you will be happier at the end than you would have been if you had not.
"She is clothed with strength and dignity; she can laugh at the days to come" - Proverbs 31:25