Implantation bleeding please help?

Hi my cycle is usually 35 days long, today is day 28 and when i got up this morning i noticed brown discharge when wiping i havent had to use a panty liner its been there all day just when wiping, i thought it was my period coming as i have lost about 10 puonds over the last 2 weeks and thought my period might be regulating itself, so me and my dh bd'd a while ago because that usually brings af on for me if i feel its coming and nothing just a little brown discharge, but by my opk i ovulated over 2 weeks ago so how could implantation only be happening now if it is that, did 2 pregnacy tests a couple of days ago and they were bfns thanks for any advice in advance xx has any1 else experienced anything like this and was actually pregnant