Becasues your are overfocused on your hands and holding your breath. You must monitor your breathing and RELAX.
becouse you're not used to energy manipulation ??...
first train new, when you have some skill train psi balls, after training new for one week i could feel my psiballs, clearly, and even send construct to a friend (that's two weeks, though), but it's different for everyone
your body is not trained and underdeveloped, if your head starts aching STOP RIGHT AWAY, the same with intense burning in hands, or wherever you make your psiball
+ i agree with what rastus said, chill out
Use a source to draw energy upon.
The Sun, The Moon or the plastic mug for example
I don't tend to use my own energy often I use it from sources like Mystic Cloud said, it zapps less energy out of you and you can go on for longer. The sharp stabbing pain probably isn't an energy thing probably strain on it or something, I don't know I'm not an expert in these things. When your light-headed it can be because of a lack of oxygen or too much (in this case it's probably lack) so try and relax, and just let the air flow into you and the energy flow from your source into the psiball and it should be easier to breath that way.
Sorry but i seem to be taking over General Metaphysics but. Just now i was trying to create a psi ball. After about a minute, i felt it was hard to breathe, a sharp stabbing pain in my lungs. Then i got light headed, my mind began to spin,i nearly fell backwards and fell unconscious. Can someone please tell me what on earth happen then!?