What do you mean by “finding the Ip address”? Also, what do you mean by “changes to the alternate IP address”? We need to know if you have a hard coded IP/mask and the address of the router.
If you are using DHCP and you end up with an address in a range you didn’t expect, you may have two DHCP servers running on the same wire. Many of the entry level/home routers and APs default to being DHCP servers.
I can’t really help you without more information.