Late period

I am going on day 14 of no period. I am not on the pill but I had sex dec. 20th. I was supposed to start my period Jan 1st but never did. So I took two pregnancy tests and a home one and they all said negative. I have been extremely hungry it’s like I eat and than 5 minutes later I am starving again and I weighed myself and I go from 110 to 107. I can’t sleep, my muscles get sore and my back hurts sometimes and I had a lot of clear discharge the week of ovulation but now I don’t have as much and I have head aches so why could my period be late?