I need help and advice

Ronna • SAHM to my amazing 3 year old Princess. Baby Borja #2 on the way. Due 12-31-17
So we h my MC i keep getting faint line up until the day of missed period and it was so light... 
So fast forward here i am in the same boat, the line is there but not getting darker, isn't it suppose to get darker every 3 day??? I'm a mess... Anyone have this happen and everything turn out ok???
Any advice would help.. Thanks