Your doctor needs to order a stress test for you. This is when they have you to on a treadmill and exercise and see what's going on. They check blood pressure and heart rate. There are things such a a heart problem you were born with that is keeping enough oxygen flowing through your system when you exercise. I am not a doctor so I can't say this is for sure bit I do know enough to tell you you need to insist on a stress test. I wish you luck.
The headaches and vision loss are serious symptoms. Maybe you're just dehydrated, but there are also some dangerous conditions that can cause this. These conditions are rare in a young person, but not unheard of. See a doctor ASAP, to make sure that vigorous exercise is safe for you.
For me the symptoms spell migraine, just like I have them. But I never had them after exercising though. See a doctor and ask him. Hey, if partial loss of sight does not prompt you to ask a doctor, what the hell will?!?