Hi,I Found Out I Was Pregnant In September Which I

Hi,I found out I was pregnant in september which I kept bleeding on and off..did ultrasound at 5 weeks 5 days which they were not able to locate a fetal pole etc...belive because pregnancy was young I was advice to repeat U/S 14 Days...during that time I kept bleeding on and off which I thought was implantación bleeding because it was not heavy...went to a gyna and the did the blood HCG ptest, which it showed HCG was below 1500,was to repeat it 48 hours but started having pains,bleeding etc so I went to a doctor near which he confirmed am having a incomplete miscarriage. He performed a D/C with pills....I went back a week for check up he said everything looks ok I just have a little tissue left which he used a tube suction to remove the remaining tissues.... on October 12 I started having severe pain in my rightside and started to bleed which I took as a period..pains got worse I went back to the doctor he did a U/S and said he saw ntn in my womb or in my tubes....On the 13 I started vomiting,bleeding and in worser pain he did a ptest and it still showed I was pregnant,I was rush to hospital to see whats the cause of pain...while their doctors run checks in the evening I was informed that their was a mass/tissue in my right tube resuling into a rupture of my right tube due to an ectopic pregnancy....I was rushed to the theater where I was operate on and the tube removed....am confuse as to how did the doctor I went done an ultrasound but saw nothing in my tube,did a D/C gave me medications after but something was still in my tube growing that it created damage...thought I was ok please give me some advise as to what may had happened please.