Wifi not working on PC

I have a PC. Windows 10, I have been having wifi troubles with it. Our plan is supposed to be getting 600mbps- we got the new modem a couple months ago and it seemed the connection got worse on my computer. I called to have someone come out and see what the problem was and they replaced the modem and the connection on my phone is now getting 300-400mbps when it was getting around 90, but when I test on my computer I can BARELY load a page. It takes me 15-20 seconds before the page even loads and sometimes not even that. Sometimes it just says I have no connection. Why is this happening? On my app, when I troubleshoot every device other than my PC it says “strong connection” but when I test my PC it says “fair connection”. I need a better connection on my computer as I do work from home majority of the week. The modem is closest to my computer, it’s too far to have an Ethernet cable but I’m confused as to if my computer is closer to the modem than my phone or other devices, why am I getting a worse connection?