Virus took over : browser keeps redirecting to yahoo, camera/email/imessage etc not working

Hello !! Forgive me for some potential grammatical issues, as English is not my first language.

I'm having some trouble with my MacBook Pro 2017 running with High Sierra (if that is relevant).

So, its been a while since I noticed this problem, but never really thought much of it, but now its freaking me out. Like seriously.

So it started off with everything I typed in safari's search bar redirecting me to yahoo search, even though my default browser is google. It really is annoying, and when I check safari's extensions, nothing shows up for me to delete.

Then all of my email adresses disconnected from the mail section, and I can't seem to reconnect them, same goes for iMessage and iCloud.

Then my camera stopped working, whenever I click on the photobooth app, the little green light turns on but the screen stays black, and when I close the app, the little green light stays on for an additional 5-10 seconds. This is what is freaking me out the most, im scared I've been hacked and might be observed. I might be a little paranoid, but we never know.

I can't really buy an antivirus right now for some important (and good) reasons, so I would love to know if anyone has faced these issues and could eventually help me find a way out.

Thank you so much !