New nursing student...light headed when seeing blood?

Ok, im a new nursing student and i started clinicals today. I have always been fine with dissection, recieving shots, and seeing blood with skinned knees and such. BUT, i get light headed when I see blood being drawn or me giving someone a shot. Today for the first time, I took a pt's glucose levels. I was actually fine giving the prick, but when I had to scrap the blood onto the tester myself, I got really dizzy and sick. Now im nervous about giving shots, IVs, and doing more of this kinda stuff. I dont understand why I have a problem!! I want to do this stuff and I find it interesting, but I get dizzy!! Help, how do I overcome this?!