Possible Virus that I can't get rid of.

Oct 5, 2018
I recently formatted my laptop and reinstalled Windows 8 because my system was displaying odd symptoms, such as high disk usage, lagging, and a strange pop up on Facebook. I did full scans on the laptop with Kaspersky AV, Malwarebytes, Superantispyware, HitmanPro, but I never received any bad results. So, after formatting my laptop I made sure that Windows Firewall was on and then I performed full scans using Kaspersky, Malwarebytes, and HitmanPro, but again, nothing was found, but I keep getting this weird pop on Facebook that says Not Logged In Please login to continue BUT it has two buttons cancel or continue...and when I had clicked on it in the past before formatting, it never logged me out, and I just thought about the fact that the genuine Facebook pop up does not have a cancel or continue button it (it will just display the log in button), so I'm 100% certain it's a phishing attempt or something, but what I don't understand is how it's getting on my laptop. Any help would be appreciated. I just want to make sure that I haven't been hacked.

PS: Before any of this started happening I had tried to download something to my phone from the playstore but noticed after that anytime I'd download a new app it would uninstall itself, so I installed Avast and did a scan and it detected that one of the apps I had downloaded was malware and it deleted it, and ever since then I haven't had any issues with my phone. Could that have something to do with this?