Spotting During Pregnancy. Pelvic Exam Showed Closed Cervix. Decreased Hormone Count. Meaning?

Hi, I went into the ER yesterday morning for spotting or light bleeding. They did blood work and an ultrasound and said everything looked fine. My hormone count was at 1400 and the uterus was visible with a dark sac inside. They said i was about a month along. There was no evidence of outside bleeding n the doctor said I should be fine but to come back if the bleeding worsens. I went home and the bleeding got worst so I went back in. They did an ultrasound n there was no longer anything visible, however the pelvic exam showed that my cervix was closed. The blood work also showed that my hormone count dropped to 1185. They didn't say it was a miscarriage but said it was a threatened abortion and that I must go back in a week. So my questions are, what do you make of all of this? How can I prevent this from happening in future pregnancies? What may have caused this threatened abortion? What are the risks if the pregnancy goes to full term, despite all these complications? How early can I get pregnant again following a miscarriage? Are there exams or tests that I should take to see if there is something wrong in my physiology that isn't letting me carry this baby to full term?