Next time you go looking for porn, please stop clicking on all the adverts.
Suspicious email? Don't download anything.
Random pics of hot guys on the sidebar that "want to hook up in your area"? Please look away.
In the YEARS I've had my own computer (that no one else was allowed to regularly use) I've never gotten a single virus/trojan/etc. It's not that difficult.
Also - might not be a bad idea to just run Malewarebytes anti-maleware a couple times. Might catch a few things.
What antivirus are you using? (I'd suggest Avast as I'm rather sick of AVG right now and don't really know others too well. Paying for antivirus is just silly)