Implantation bleeding?

Hi! So my cycle is regular every month. It is always spot on to the T. We have been trying to conceive for 4 months now. I ovulated 3 days later than the predicted date this cycle. Making it day 18 —we had sex according to the fertility window as well. Now I am 3 days late for my period and have some SLIGHT brown when I wipe. 0 period symptoms whatsoever. My pregnancy test was negative also. Is this implantation bleeding? Is it the start of my period? Although this has never happened before like I said, my period is always on point.... Am I testing too early for a result? Someone please help!