Bear with me!

I am desperately trying to figure out when I become pregnant. I am so so confused and my appointment isn’t until September 20th. So maybe you ladies can help me out. I got my first positive on the 8th of August which would have been 9 days before my missed period of this month! And it was very strong immediate lines. Last month I had a five day period but it was not heavy and clumpy like my usual periods. Is it possible I was pregnant last month and not getting positives and got what seemed like a period?! I just don’t understand if I got pregnant this month how I could get such a clear positive9 days before my missed period. Any help understanding would be great! Thanks ❤️