Imolantation?

Can anyone help i have a 28day cycle period usually start on time and last 7 days heavy the first 3 with bad cramps where I'm in bed and then light for the remaining 4 days. My last period was 4th May af due 31st I had light pink spotting on the 26th and 27th witch then turned to brown spotting on the 28th i even still had it when af was due it hasn't gotten heavy and I javent experienced any cramps at all just bad back ache on and off my sister in law said it could be implantation and that you can have spotting through pregancy its very common I took a test on the 1st June (still spotting) but my husband said it looked like a bfn but I swore i saw the faintest line you just had to squint haha she said retest in a week I've had this spotting now for 9 days but it looks like it's disappearing next to nothing im a little confused cause I already have a 5 month old and never experienced inplantation with him just a missed period and got bfp 4 days before af any advice would be wonderful thank you