I haven't been able to keep up with this site because the other ones keep my attention. I'm working on it though. There is a way to know, I think, if you're doing enough cardio. What is your goal for cardio? Are you able to maintain a decent pace? In other words, let's say you made a deal with yourself that 2 miles in 14:30 was about right. You'd like to run it faster, but any slower wouldn't be what you want.
Can you maintain that pace? If so, you're doing okay, cardio-wise. If your goal though, is to lower your time, you have to just keep monitoring it to make sure you're on the right track.
Hope that helps.