late period because of eating?

I'm going throught the same thing! My period is 6 days late and I've never had that happen before. I've taken plenty of pregnancy test and even got a blood test taken and they are negative. I am currently 109 lbs and I lost 7lbs in 6 weeks. I was eating enough calories but working out 6 to 7 days out of the week. I'm hoping my diet and exercising is why my cycle is all out of whack. I am going to my doctor on Monday to pick his brain.