Motivation to Exercise?

I'm not overweight at all, and skinny by most people standards, but even though I'm skinny (5'3 115lbs), I'm very out of shape. The meat I do have on my body is all flab and I'd like to get toned a bit. I used to be very into exercising, used to do yoga everyday...plus exercising on top of that like 5 times a week. That was when I was a teenager, now as an adult when I feel it's more important to keep a healthy metabolism and such, it just seems now I have a lack of motivation just to even start again. It seems being healthy should be motivation enough, but it's not. I think about waking up 20 min early to get in a little exercise before work, but I can't move out of the bed in the morning (not a morning person)...then I think about trying to fit in some exercise after work, but I'm just am too tired to do it.

With all these excuses I have (haha), how do I just get the motivation to be healthy again?

Help! Any words of advice or encouragement would be appreciated.

Thanks in advance