Talk to Gynecologist on Conception

i concieve but just after 1 weak it ends automatically . whenever i check my pregnancy through strips it shows positive but a faint line. after one weak of missed periods it starts spoting first then after full day of pain a membrane comes out and bleeding starts. this time when i consulted a doctor she fist said its iregular periods but then during ultrasound she said its conception but wothout fetus. and its position is very down .plz help me to understand my problem. it has happened to me mant times