I had what seemed like my period, but could it have been implantation bleeding. it was lighter than normal.
This means something different for everyone. Did you need a pad or a tampon at any time? If so than it is very unlikely that it was IB.
If not, then there is probably the slightest of slight chances you could be pregnant, but with the negative tests it is unlikely. Test again in a few days if it makes you feel better, but don't get your hopes up.