Hey I'm Becca and new to glow but could it be possible to be pregnant with using the withdrawal method? Just with pre-cum?

Sorry for the TMI, I am just wondering because my bf and I use this method (allergic to latex) and my AF last month was very different then my usual AFs, I have a normal cycle 28 days but last month my AF was and nothing. AF was late 2 days but then i had light pink spotting for 2 days not enough though for a tampon just when wiped then bleeding for 2 days then more spotting but instead of pink it was brown and not a lot just when I wiped. I've talked to my friend and she said oh your pregnant but I have taken 4 tests all negative. I've read about decidual bleeding but I cannot be sure. Plus I still had all the symptoms minus the sore breasts. Anyone else experienced this and was pregnant?