Ok I was thinking about this today when I was on the treadmill at the gym...

I wear one of those heart rate monitors when I work out. I have noticed that I have to work out harder and harder to get my heart rate up when doing cardio. I have been going to the gym for a month now and go six days a week. I do a light cardo and lift three days a week and do a full cardo workout three days a week alternating days. I have tried all the cardio equipment to see if I can get my heart rate up but it seem like I have to work too hard... when I say too hard its like I cant push myself to do it. So I guess I am asking two questions.

First am I just being lazy and need to push myself? Can you push yourself too hard?

And is there anything I can do to get my heart pumping with out pushing myself?

Hehe I hope someone understands what I am talking about this sounds so dumb!
Sarah