The internet speed is extremely slow only in my PC

Hello everyone, 

The internet speed is extremely slow only in my PC while the other devices working perfectly. The average speed with the other devices is 90M, while my PC is only 1M. My PC used to be fine and I don't know what happened to reach this problematic situation. 

What I have done? I searched the web and as a result I checked the hardware in my PC. The hardware test found nothing wrong.

I also uninstalled the driver of Intel Dual Bank Wireless AC 7260. I then installed the latest driver available. What happened? The speed went up to the average speed (around 90M). However, after only few minutes (less than 5 minutes), the speed was back again to around the 1M speed! This gave me the feeling that the problem is not a hardware issue and I'm not sure. I have to say that I repeated the re-installation several times and every time the speed goes up to the normal speed before falling down.

I also scan my PC for any security relevant issue, however, nothing was detected. 

My question and hope is what should I do? Change my hardware itself? Should reinstall my windows? What do you think please?