Why is this happening?

Hey everyone. First post here.

I just want info and want someone to read this and possibly explain to me

Iv been climbing ranked maining support. Not trying to brag or whatever but I often get complimented in game on my supporting and I think I do a good job and play it competently.

Iv been on a huge win streak and had a very high win rate. I started out in silver 3. I eventually skipped ranks from gold 3 to gold 1.

I got into promos to Plat. Had 2 afks two different games and lost promo.

After that, iv been on an enormous lose streak. Iv dropped from gold 1 to gold 3. I just keep losing.

I take long breaks and come back and play a game and I lose again.

It's not normal for me to lose like this, this much. I really don't know what I'm doing wrong. I'm doing nothing different and I honestly think I play well.

What can I do differently? Why is this happening? I'm open to criticism and any info.