what should i check if my mac is running a little slow

My Macbook Pro has recently been a little slow. I get the pinwheel image frequently and I’m hearing the fans kick on. Granted I’m a heavy duty user. I have photos, safari, calendar, messages, evernote, and Quick books online mac app all running at the same time any given day. I noticed it when i opened a preview of some blueprints for a building and it just had a very difficult time zooming in and out and panning through the blueprint on preview. Again all of these other apps are open simultaneously. I would like to know if there is something I can check? Maybe something running in the background i don’t know about? Any advice would be great. This is late 2013 macbook pro retina 15” w/ 16gb ram. I also recently upgraded to the el Capitan and It hasn’t done it yet. Its only been 1 day tho.