Spicing things up in the bedroom?

I've noticed these past few months, my husband's sex drive has gone down. We barely have sex anymore and when we do, he skips the foreplay and goes straight to one position until HE finishes. Which always leaves me pretty upset and frustrated. The times that I've tried initiating sex, he almost always denies me which leaves me feeling rejected so I just never try anymore. I've told him how I felt but he just brushes it off :( 
Has anyone else been through this? We've been married for 4 years if that makes any difference.