So I received several notifications at the same time indicating "-2" in different answers of mine (old and new). I never understand why this happens. Is it that somebody is skimming at my answers and downvoting me every time? Is it a user that was banned and the positive votes were erased? What is it?
I'd preface this by saying that I don't see a particular reason why you got those downvotes all on the same day. The answers, at a glance, seem OK. Maybe a moderator or admin could have a look to see if you're being downvoted by one individual. I'm neither so I cannot investigate further.
That said, as far as I recall the system automatically detects when someone is going through one user's questions and voting on them. This (apparently) happened me in the past and the system will automatically reverse them if it detects them as such a pattern, which it did do sometime later (may have been days) in my case. So maybe give this a few days.
It's not uncommon to get votes up or down out of the blue on older questions and answers. That's pretty much the site working correctly as it's supposed to keep old questions and answers to help peopel with the same or similar problems.