How can i stop someone accessing my FB account from the same ip address i keep changing my password
The IP address could be yours and you may not know it. From each device you use facebook, go to our homepage https://www.whatismyip.com to see if you have IPv4 and/or IPv6. Compare what we show on each device to the IP you're seeing on FB.
Another option is to copy the IP you're seeing on FB and do an IP address lookup https://www.whatismyip.com/ip-address-lookup/ to see if the IP is in a familiar area geographically.
The last option is to check to make sure your device doesn't have a keylogger installed. You can check this using Malware Bytes. https://www.malwarebytes.com/