My Period Is Around About 4 Days Late, I Have

my period is around about 4 days late, I have been suffering from lower abdominal and back pain for almost 7 days now with the tiniest bit of pinkish discharge on a towel that I wore in my underwear expecting my period to come and the pains can be reasonably strong, my nipples are incredibly sore I have been getting heads aches and my bowl movements have increased a lot I took a test yestaday and it was negative I conceived and had unprotected sex on the 7th December and my period in expected I think around the 18th December .. Please help