Is it normal to get a big losing spree after having a sustained high win rate?

So from silver 3 to gold 1, I had 70-80% win rate playing Janna and Sona. I climbed fast, in about 1-2 weeks so it was all in the same patch - I'm not being screwed by item changes or anything. I'm talking a consistent 70% win rate over about 50 or 60 games. But now it doesn't seem to matter what happens bot lane and I have a 35% win rate. It's also frustrating that I can have a plat 5/plat 4 MMR, but get demoted from gold 1 down to gold 2. If my MMR is in plat, I shouldn't be getting demoted to gold 2. Makes no sense. I don't like blaming my team but when you main support you kind of depend on them. Don't tell me to play another role or different champs, I'm not asking for advice on how to climb. Also, Sona and Janna both have 2 of the highest win rates currently. I'm just asking if this kind of match making is normal? If so I guess I just have to wait for it to even out.
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