-34 LP? huuuuuuh?

When you hit 100 lp, your promos still add or subtract lp based on those promos. If you win one and lose two, and you normally gain 18 lp for a win and lose 16 for a loss, you should come out with a net gain of -14 LP. Likewise, if you're losing -17 lp for a loss, lose both promos in a row, and don't win anything in your promos, you'll end with a net loss of -34 lp and come out with 66 lp after you're done.

Hope that helps!