Wifi randomly super slow

[Cars Canadian]

Hey so I have coaxial internet to my house, its 150 down and 20 up, on my computer I get around a megabyte per second download and about .10 upload. On my phone in pretty much the exact same place I get around 60-90 down witch is normal for being a floor above the router, that's another thing, its pretty much impossible the run ethernet because I do live with my parents and they don't want to put holes in the drywall. I believe this is an issue with my network card (Realtek 8812AE Wireless LAN 802.11ac PCI-E NIC) but I just want to verify that it is the issue before I buy I new one. Yes the antennas are adjusted properly as per the manual