Internet connection very slow only in my house and only with my Mac
Internet or Wi-Fi problem
Open System Preferences... > Network > Wi-Fi > Advanced... > TCP/IP
and note the IP address of your Wi-Fi router.
Let's say it is 192.168.1.1.
When you are in your bad network situation,
open a Terminal
and enter the following command:
ping -c 100 -s 1992 -q 192.168.1.1
to check your Wi-Fi quality of connection and let run this command for nearly 2 minutes. Make a copy of the result and include it in your question.
If is tells 0% packet lost, then your problem is a general Internet problem. If it tells your that you have some packets lost, then your problem is on the Wi-Fi side.
I suspect that this might be your case.
Analyse a Wi-Fi problem
Download the iStumbler software:
iStumbler
This version is free:
iStumbler 99
This is an excellent quality software and running without problem on from Snow Leopard
to Yosemite
(I didn't yet tested it on El Capitan
or Sierra
).
When you are in your bad network situation,
let iStumbler
run for 10 minutes, order the output along the Level
column in decreasing order. Make a screen capture and include it in your question.
IP or DNS problem
Open a Terminal
and enter the following command:
dig www.apple.com
This command will ask your DNS server how it does resolve the www.apple.com
in an IP address.
Include the output in your question.