I am a paramedic student doing my clinical rotations and im getting a little discouraged. I have set 5 Iv's all of which I am getting good flash, however I have blown 2 of the five and the others im not feeling a valve in the vein but when I go to advance the cannula, it goes in just a tad and I hit resistance and an unable to advance any further, I tried to flush and advance incase its a valve but its still not working please help. any tips would be greatly appreciated.