Does punching a Heavy Bag build muscle?
hell yes it builds muscle, but no you will not look like a body builder. To develop good punching skill you need to balance your training with shadow boxing, bag hitting, and wall pad hitting. The wall pad cant be done too much or you'll get slow, but it will build the best power. Too much shadow boxing will give you great speed but tendinitis as a side effect. The bag is a balance of speed and power.
Is it normal to have a headache after sparring in boxing?
Not normal, though if you have weak neck muscles the chances of a headache after sparring will be more of a probability. The headaches come for the snapping of your head back and forth and sideways, when the head is pushed back with force from a punch, the air and blood supply going to the brain through the carotid arteries is constricted, this will cause lack of air to the brain and sometimes will not show up immediately. Try to build the neck muscles by getting some special weights that attach around the neck, move your head forward, backwards and sideways daily for about ten minutes. You can ad more time after your neck starts getting stronger. "The stronger your neck, the less headaches".
I train Boxing very hard but when I get in the ring for sparring I fill heavy and slow and get tired in less then a minute can someone tell my why?
You likely have been training, but not training for actual conditions. I made this same mistake when I started I would run, heavy bag, shadowbox, etc. all the things to be strong and fit, yet when I went to spar none of the work I put in showed. At my gym there are professional boxers. I often watch them just to see how they train and one thing Stuck out. They don't train at a constant rate. Instead of training at a constant rate for 3 minutes and resting for 40 seconds, they explode for 30 seconds, then practice at their normal rate for 30 seconds during the 3 minute training round. When we went out to do roadwork, they would run at a steady pace for 2 minutes, then explode and dash for 2 minutes, rinse, repeat.This training is effective for 2 reasons: It simulates a real boxing match. Boxers aren't usually boxing in a round for 3 straight minutes. There are high points of activity and low points of activity in a round. They go at a normal pace then switch to overdrive.It develops an important skill called active resting. Good boxers can go 12 rounds because they have trained their bodies to rest when they are working normally, and between the explosive bursts of energy. It's also a way to conserve energy instead of going all out for 3 rounds then run out of gas.If you want to have energy during a sparring match you need to put your body under similar conditions so that it can get used to it. Let me know if this was useful!