Iam new to boxing within the last few months and realy injoying it. Ive been into fitness like road running and weights ect for years an consider myself to be very fit an in good shape. The prob is after 2 /3 rounds on the pads or sparrin im burning out. My Question is what traning should i be doing to be boxing fit and stop burning out so fast.

boxing fitness is like nothing else isn't it?

Just look to push yourself by doing sprints, great for cardio and that feeling like you're going to puke!
Circuit training is also good.
One key thing is try and relax, being tense will burn you out.

Don't forget you will have your own pace and rhythm when working by yourself on a heavy bag. Pads/sparring breaks that and pushes you to work harder. I'd suggest if you're working rounds on the bags try doing one at your natural pace and the next go for it more. There are tons of things you can do you're still a baby in the sport. Enjoy!