Implantation bleeding? (Possible tmi)

Ok so I'm on CD27/12dpo. First time on Letrozole after ttc for 2years. Cycle is ALWAYS 30/31 days, for the past 3 days (10-12dpo) I've had mild spotting, it was very light pink barely there on first day, second was slightly heavier still pink and today its more brownish. I've also been exhausted in the evenings and have had cramping mostly on left side. I would never normally have spotting or cramps this time of cycle. But then I'm not sure how my body will react to the letrozole. But does that sound like it could be implantation?