Well, there are available resources to people without a proper diagnosis. If you're not understanding the material, Professors/TAs are required to have Office Hours (well at my university) and there are usually tutoring resources on campus you can sign up for. Often times if you shoot them an email and say something like, "I've come to class but don't understand this concept" they'll gladly email you back OR see you in person if that's what you prefer.

Since college education costs so much, trying to get the best out of it is important! :')