Hello ladies, I am new to this and hoping for some real life situations rather then Doctors books to what should and shouldnt happen..!

So i was 6 weeks pregnant when i miscarried around the 1st/2nd feb 2013. I had a scan the following week on the 7th feb and was told it was complete and all was gone....However i took a tes 4weeks after and it was still showing positive, so i was sent for Blood Tests on the 5th and 8th of March 2013, these showed a drop from 5000 to 700 hcg i was told i am not pregnant,... However here i am 18th march and its still showing positive 6 and half weeks later...I have had some very light bleeding the past 3 days for a bit in the morn then it stops for the rest of the day and night and starts over, no clots or pain and still a positive test....Doctor is COMPLETLY CONFUSED..! I went for more bloods today so will see what they say...Is there anyway that i am preg and they dropped hence the little bleed but are on he rise as a new preg?? im also :/

any info :)