Any tips on staying loose and relaxed before sparring?

I sometimes have the same problem. I tend to get very tired during the first 2 rounds. But when ive taken a few shots and get warmed up again its no problem. Its like a get pshyced up

 

A lot of factors come into this. First, weak muscles tense harder than strong ones. Make sure to develop the ability for your muscles to endure long and tough activities like boxing sparring. Second, I recommend mental exercises as part of your daily routine. If you are a serious boxer and training hard physically, this will pay dividends in the ring. I recommend Gold Medal Mental Workout for Combat Sports. Learn to relax your muscles and target your concentration on the task at hand. More practice at this will also help.