Icloud

Hi, at least once a week or more now someone is signing into my Apple ID I keep getting emails saying somebody had logged in on another device when it wasn’t me. I find myself changing my password like 3 times a week because I can’t download stuff because somebody is changing my password. How can I stop this? It also scared me as they can access my pictures and someone on social media has been threatening to post photos of me that are no where other than my camera roll so I’m wondering if it’s the same person as that it the only way they could have access to them