Ttc could i be pregnant

My cycle are normally 28-29days last month I came on on time I tho it was af but I only spotted for a day and a half my periods last normally 5 days first day spotting 2&3 heavy 4&5 light took test negative went to doctors she thought maybe it was implantation bleeding she took blood and urine everything came back negative and she told me if I didn't have a normal flow our no signs of AF she wants to see me back in a couple weeks I slipped up on the last week and was like wait I might is well wait cause a AF was due the following which was July 22 and I think af came on July 24 which was brown spotting no cramping but nothing July 25 or 26 I'm so confused took a test and it was neg has anyone ever experienced this are has any advice on what they think