ADD? Please help!

So basically i have had trouble focusing in school since 5th grade and I'm a freshman now. High school is a lot more tough and you really need to pay attention and I do. I watch, take notes, ask questions, but it never goes through my head! It's not only that but I'm always kinda tired during the day and I can't keep my head up. I constantly lose things, I forget things, and I speak too fast that I combine, flip words around, or flip the first letters around of two words. I've recently looked into adderall. I've researched it a bit and I recently talked to my dad about it. All he said was no and that I don't need it. Im smart when I want to be (i always wanna be smart) but I have bad grades and I feel like I'm going nuts. What do I do?? Please help!!