Yellow/mustard spotting on panty liner

I had a sharp pain on my right abdominal side today that was enough to take my attention. A few hours later I went to the toilet and I had yellow/mustard spotting on my panty liner. I've not had any colour on my panty liner since my last period. Could it be a sign of ovulation or even implantation?? :D I don't actually know when I ovulated as this is my second month off the pill and I haven't got the hang of OPKs.