how long does implantation bleeding last?

I was trying not to track things (as much) this month just to cut the stress and little. I have been debating posting anything actually because I don't want to get my hopes up but I honestly can't get it off my mind, so please tell me if it could be anything else. So at 7dpo I had light pink spotting (started in the afternoon) the pink carried on until about 11 am the next morning and then it turned brown and continued for another day and a half. I have never bled in between my periods so it brought up some alarm. For a while I thought maybe it was from the internal ultrasound a had gotten but the spotting didn't start until 3 days after so I doubt it was from an irritated cervix. I don't know, what do you guys think?