could I be pregnant?

I recently got put on nexplanon but I still have had sex without condoms a few weeks ago. Yesterday I randomly started getting brownish light discharge, I knew something was off because I never get that unless its the end of my period. I looked it up and I found something called "implantation bleeding", has anyone ever had experience with this? Could I be pregnant?? or do you think its a side effect of the nexplanon?