Hi there @ozgurtagay & welcome to the community! What traffic are are you referring to... traffic from Pinterest to your website or your monthly views at Pinterest or something else?
I'm experiencing the same issue! After the 13th of December, my traffic drops by about 50% and then continues a downward spiral from there.
At first, I thought it might be a seasonal fluctuation, and maybe my niche wasn't as relevant around Christmas time.
However, from my analytics, I see that my niche is doing fine, it's only pins with my domain name (pinned by myself and others) that have taken a dive!
I would appreciate any help I can get on this, please 🙂
Please see attached screenshot. Pinterest profile: https://www.pinterest.com/HibiscusRoots/