These kinds of things can oftentimes be overcome through psychological habituation, or the act of exposing yourself to the target of your phobia in small doses over a period of time. Kind of like the reverse of getting off of an addiction.
Pretty much any trained psychologist can help work you through this, but a lot of people are successful without professional help. In your case, though, I would enlist the help of a friend. It's hard to type "blood" into google and end up with small doses of it.
I'm not going to suggest any specific plan, since that would probably constitute unlicensed medical advice of some sort, but you can probably figure something out that works for you. Or, if you have a school psychologist, they might be able to help as well. But it's really not something you need to worry about affecting you forever if you take steps to overcome it now.