I'm 27 and work out a lot.i've always had palpitations but lately my heart pounds a lot and i get short of breathe.also i've felt weak. what is this?

Check up: See a cardiologist for evaluation for atrial arrythmia said which would be more common at your age if you take excessive stimulants and or don't get enough sleep. Best not to delay and miss something important and or fixable as your symptoms are significant!

Rule out heart probs: Your symptoms sound exactly like mild panic attacks/anxiety. But before you can assume that,you should have testing done such as a stress test & a medical exam. Once you have had any physical causes eliminated, you can assume your symptoms are caused by anxiety.There are many solutions: stress reduction courses,therapy,meditation &just knowing what these symptoms are,-all can relieve your worry!