She denies me sex!!!

I am 34 years, married to a 28 years old Lady. Whenever I ask my wife for sex, she'll always refuse. Its once in a long while that she will agree to have sex with me. I trust her, she's not the kind of woman that will be flirting around. Since we got married and got blessed with a beautiful child, that's when I started seeing this funny and strange attitude in her, and i love sex so much. I don't want to cheat on my wife. I have talked to her many times that she might push me out there, and make me cheat on her, yet she doesn't care. I don't know what to do Please advise me.