Spotted? TTC

ok so I've started taking fertility supplements this month. My opk test came back positive April 11th. BD April 11th then, April 13th at night, then spotted on April 14th. I never spot unless I'm starting my period (period isn't due for another 11days). we didn't have rough sex either. so my question is do you think I spotted due to ovulation? because it's too early for implantation bleeding ik that. what's your educated guess? I'm just looking for answers cuz I rarely spot. it's really rare for me.