Why is my GE side-by-side refrigerator getting warm in the frig part but the freezer still is very cold?

Hi there.... I have a side-by-side refrigerator and the freezer works great but the frig part doesn't stay cold. I defrosted the whole refrigerator (by unplugging it and putting pans of hot water in the freezer part) about 3 weeks ago and it worked great for a couple of weeks but now the frig part isn't as cold any more. I was thinking that it might be the automatic defroster that would cause that... but I wanted to get some feedback before I invest $80 in the part. The frig is only about 5 years old. Thanks for any help