So, neurological issues can cause this. We have what is called 'motor planning'. This basically involves our nervous system and how it communicates with our muscles. At 17, you probably should talk to your parents about this and ask their advice. They will probably take you to the doctor and you can explain what is going on. by the way, how long has this been happening?
Sounds like something you need to talk to your doctor about- many things could be causing this (the way your brain is processing, possible a muscle issue, etc) so get to a doctor and explain the situation.