how do i know for sure if i have adhd

the thing is, ever since i  can remeber people always made fun of me because i was slow at resonding to questions, or just talking. and recently i found out in 2001 i have a difficulty with reading job applications , examinations, instructions, but iam able to read regular books and have no problems.  but when i went back to school in 2001 , bryman  collage for dental asstant my teacher realize i have a reading problem when test came up, i was passing all my classes , but when the final test came i failed it, the teacher knew me and that i was doing well , but could not understand why i failed, i told her that my teacher said i had a reading problem  and to talk to him, and she did and i took the test oral and pass. sometimes when people want me to do something i need them to explain in detail and it annoyes people, or is irratated because i kindaof talk to much and always nervous and dont know how to relax and too sensitive to peoples responsives ,i get upset to quickly . some people think because i act the way i do that i act like a big kid and to hyper.  i feel different then other people because i take longer to understand or don't understand at all and they get impatient with me.all i know is i am a good person and always want to help,but people don't understand and make me feel bad because i am not quick enough for them. i lost and i need some guidance and direction.  also in the 3 years i have been having anxiety attacts and  i need some balance back in my life. please help.