Engineering is no walk in the park for anyone. With a C and two D’s, you are closer to making it than you realize. You just need a little boost to get you over the top. Reach out for some support, and bear down on your classes. Talk to a counselor and the tutoring/academic support office.
Read the chapter before the class and mark it up with highlights and questions. Khan academy can be helpful if you are stuck.
To prepare for exams, be sure to get copies of old exams and practice, practice, practice.
You have to believe you can do it. You can!