Three weeks ago I was 8 weeks pregnant I had what I thought to be a miscarriage now its been almost a month and I have a posiitive tes how long does i?

See a doctor. You need to be evaluated professionally for an answer to this question, and good luck.
11 weeks now. Well, you said that 3 weeks ago you were 8 weeks out and so now you are 11 weeks. Spotting/light period is quite common during early pregnancy and so many women think they just had their usual period and thus not knowing they are even pregnant. Having some bleeding is concerning to many and thus believe they had a miscarriage etc...In your case, maybe it was just spotting. Congrats. Consult doc.