Yellow tinted discharge?

My period is 4 days late and the last week I have been experiencing light cramping in my lower abdomen and today I notice clumpy yellow tinted discharge. I took a pregnancy test yesterday morning and it was negative. I've heard that a yellow tint in your discharge is a sign of pregnancy? I don't know how true that is, but is it a possibility that I could be pregnant or could it be a yeast infection? But it doesn't explain my late period... I've never had a late period. Ever. Has this happened to anyone?