Every now and then I get what feels like a rush of blood through my heart.. like my heart is trying really hard to push the blood through for a second.. it doesn't last long.. but it is scaring me and makes me very nervous. I'm only 17 please help! What is this!

It could be a number of things like heart palpitations, irregular heart beat and worse.
If it doesn't feel right to you then you need to get to a dr.