biglouis and Mollygo, I think I can answer your questions:
When you connect to the internet your device is allocated an Internet Protocal Address, an IP Addess, this address is only
allocated for a short time and after a period of inactivity this address will change, there aren't enough addresses to permanently allocate an address to every device on the internet.
Due to the way the internet works, you are unlikely to be allocated the same address eaach time you connect, if you are lucky you will get an address in your local area, so everything is seamless, but, if your local area is busy you may be allocated an address in a different area, for example, I live just outside Lincoln, but I often get an address in Nottingham.
It's not just your local area that can be busy and cause the issue, your connection request will go through a number of computers to get to your required destination, think of it like posting a letter, it goes through variou sorting offices to get to the addressee, computers are the same, just electronically.
Hope this helps, I've tried to answer your question without being too techical.