Everyone has strengths as well as weaknesses. I don't think that anything is wrong with you because you have challenges in this area.

Most colleges try to turn out people who have a well rounded education, including things that do not appear to directly relate to their chosen field. You say that you do great with things like technology and science so I'm going to assume that your chosen field is related to one of these fields. Knowing how to communicate your ideas effectively is important to your success, and writing is an effective and critical way to communicate.

For instance, my strengths lie in math and science. I just recently wrote a proposal for my job on 'photochromatic manipulation', an idea way outside the box in my industry but one that was greeted with enthusiasm specifically because I was able to write a strong proposal.

While I work with other very competent people, only one has been given the opportunity to set his own salary during a recent performance review. That would be me. It wasn't that I was better than anyone else, it was just that I was able to present my ideas better - and the way I was able to do that was through writing.

Like you, I am an introvert. That I get along great in a crowd and have no problem communicating with people doesn't mean that I enjoy it - but I have found value in developing my capacity to do it anyway. I think you'll find the effort expending in improving your abilities in this area will help your career.