BlurXuan, Sarah has explained what is HCG. Ya according to websites, anything below 5 is not pregnant, between 5 to 25 is equivocal (can or can be not preggy) then above 25 high chance preggy. So what you do is on day of BT, if they tell you negative, ask for the value. If they tell you below 1.2 and its already DPET14, you can quite safely conclude its true negative. But if there are some values, means got some implantation then its worthwhile to still be careful and go for repeat BT. If repeat BT shows increase or doubling, then there is a chance of pregnancy!
Chrisl, can also use heatpads daily. I assume you dont get to do acupuncture? If so all the more, good to use heatpads daily, to improve blood circulation and warm the womb, thereby improving lining also. I also took beef when getting my lining ready. And keep warm, wear socks or bedroom slippers esp for you as your climate is colder. If you can get brazil nuts, can eat sparingly too, brazil nuts aid implantation so in a way can help boost lining. And oh ya, LRD daily.