Am I exercising TOO MUCH ???

I have been doing light 30 min cardio 6-7 times a week at home for the past 2 months, but starting Monday, I have gone to the fitness center and really kicked up my work out (30 of pretty intense elliptical, then 30 min of pretty intense on bike, then weightlifting (on alternate days)). So it's only my 3rd day, but I've noticed that it's getting increasingly difficult for me to complete those 30 minutes on the elliptical. Like my leg muscles are soo stiff (I do stretch) .. and even though I decreased the intensity (from 7 to 5), it was still pretty difficult. Do you think that maybe I'm overworking myself too much? Should I switch off days? Like one day, I do high intensity like what i've been doing, and then the next day, do light exercise?

You need to listen to your body if it is physically to difficult to complete your workout then yes you need to rest your body either by not working so hard or taking a full rest day. Remember giving your muscles time to recover is just as important as exercising them in the first place. Only you can decide how much exercise is too much.

I would agree with Sublime.  You need to listen to your body.  Though it doesn't sound like your work out is a lot it will take time for your body to adjust to the increases and they should be done gradually over time.  In my first attempt to increase my work out I didn't listen to my body and ended up needing to take 4 months off due to knee pain. With the second try I started out with cardio for 30 minutes every other day and took a few months to build it up to a minimum of 90 minutes daily. 

Of course you should listen to your body. 

That said.  Working out is supposed to be hard, and it is supposed to hurt (in a good way). Make sure you get at least one rest day a week and you'll probably see results soon enough.

Be careful and enjoy your progress.

B

You should increase your exertion by 10% a week. Otherwise it could lead to injury. Believe me I know. I have to lay off running too much and too fast because of it and so am teaching extra spin classes at the mo. That been said, if you are physically fit enough to handle the extra pressure then go for it. You get what you put in at the end of the day just listen to your body, DO take at least 1 rest day and take your goals into account. Know the difference between the 'good pain' i.e muscle soreness and the 'bad pain' i.e injury. Good luck and most of all enjoy