Hi Doctor Im On My 6th Week Of Pregnancy My

hi doctor im on my 6th week of pregnancy my vaginal secretions turned to dark red but the quantity is normal
my doctor gave me dydrogestrone 10mg twice aday .. i had it aweek ago nd my situation still the same .. same back pain and cramps at night ..
1- am i gona loss my baby ?
2-my last period was on 9/11/2015 and it was regular ..how can i calculate the date of birth ?
...And lots of thaaaanx