My Apple Watch and my iPhone fitness app are not connecting, help!

My watch collects all my data movements but when I tried to see it on my phone in the app it says ‘No Data’ I can’t keep track of my goals, and my watch only tracks my movements for the day and the next day it resets to track the days movements.

ps my watch was connected to my previous phone and then I bought this one I’m using. Some apps and notifications works but everything is limited with the watch. Some notifications I don’t get and I can’t read certain messages from my watch too. It says connected and everything.