Craziness....

So I started taking Fertilaid this cycle, only used opks once a day, darkest I had was around days 16 and 17 but they weren't positive. Temp charting, and had the sip and rise like I always have, but the fertile cm didn't show till a day later. Hubby and I bd on day 18, currently on day 25 and first 2 pees of the day had brownish spotting, this last time was nothing. Does fertilaid make you spot during cycles or could this be implantation bleeding possibly? I didn't have it with my daughter so I'm not sure. I definitely don't have any symptoms of pms, so I don't believe it's my period coming early. Thoughts anyone?