Diagnosing plant health concerns over the internet is extremely difficult, if not impossible, due to the obvious lack of information necessary to make proper recommendations. If you truly want or need immediate technical assistance, please contact a professional tree service company with a certified arborist on staff for an on-site evaluation, or submit a sample from your affected plant to the University of Illinois Plant Clinic:
However, I can think of three fairly common problems that affect white/paper birch: bronze birch borer, birch leafminer, and water/heat stress.
To read more about the aforementioned, please visit:
How to Grow and Maintain a Healthy Birch Tree (USDA Forest Service Publication)