Thank you!
Hrm...I honestly can't think of anything that does exactly that: tracking your 'reputation points' over time. I've used Steem Cool before just to get a bit more detail...but that just gives the current stats without an actual history.
Only easy possibility I could think of (short of querying the blockchain for when your rep points equaled the rep level requirements) would be to ask...did you make any 'milestone' posts that included your rep level? We could find the post date on those.