im confused..

well here goes.. I thought we were expecting baby number 4. My last period was in march and in the beginning of april ive been getting car sick so ive decided to take a home ptest and it was negative at first but as the weeks went by the lines got darker and then i bought digital p test and its positive.. I literally tested like 10+ test til now, from april til now  june.. The problem was after  the first couple positive tests ive been spotting. First it was just dark brown discharged and I thought it was normal and then as time went by it became like dark dry blood then at the end of April there was tissue.. I just had the sad gut feeling that it was a miscarriage. After that it wasn't like I was bleeding bad like a regular period but just more brighter spotting.. then it became light again and finally end at the end of May.. I went to see my regular Dr. and did some blood work and the first lab results was yes my levels were high and i might still be pregnant but to confirm i have to go back in 3 days for another blood work which i did go and the results wasnt as I had expected .. My levels had decreased.. i had a miscarriage they said.. So my question is: How long before my home ptest become negative because its still showing positive.. its been like 1 month since the tissue i found..?? can they be mistaken for miscarriage??