I agree. IT WILL MESS YOU UP FOR LIFE if you don't get this reported. DO NOT BE AFRAID. What charkee said is right. Make sure you let them know you are afraid for your mother's safety as well as your own. Knowing what you know about this dude, your mother will thank you in the end. Do it for both of you. If you get DNA from him get to the hospital as soon as you can. Ask a friend to take you. The hospital staff will understand how dangerous it would be for either your mother or her thing to find out before an arrest is made, but an arrest definitely needs to happen. Don't be afraid to tell them exactly what happened. Remember this is not your fault. This dude is sick for even thinking this is okay and he's just doing it because he thinks you won't be brave enough to report it. Sometimes they know how vulnerable you are and how afraid you would be to tell your mother. That's why he's doing it! If you can't get a ride to the hospital, find a teacher, scout leader, school counselor, or an authority figure or one of your friends parents you trust ... They are required by law to report it.
The blood is from tears in the lining of your rectum. They will test you for diseases at the hospital. No worries. You'll feel so much better once he's behind bars, trust me. You'll be doing a lot of people a favor. You don't have to put up with this.