I am just curious..... If you aren't very good with networks, and cannot determine WHICH IP address is changing (WAN, or internal LAN IP), how did you determine that your IP is changing in the first place? Try to provide the following....
1 - How did you determine your IP address is changing?
2 - What type of internet do you have, and who is the carrier?
3 - Describe your network topology. (what devices are in the network, and how they are connected).