Are you seeing a therapist? It is important that you have someone to talk to about your circumstances. Also, a therapist can provide a diagnosis. Once you know your diagnosis, you can have a focus to work with.
From what you have described, you may have some type of anxiety disorder mixed in with guilt from the infidelity.
Anxiety is one of the easiest disorders to treat. You can not only see a therapist for help, but you can also work on this issue at home. Here are some resources to help you:
The 10 Best-Ever Anxiety Management Techniques: Understanding How Your Brain Makes You Anxious and What You Can Do to Change It by Margaret Wehrenberg
The Anxiety & Phobia Workbook by Edmund J. Bourne
Not "Just Friends": Rebuilding Trust and Recovering Your Sanity After Infidelity by Shirley P. Glass and Jean Coppock Staeheli
Surviving Infidelity: Making Decisions, Recovering from the Pain by Rona B. Subotnik and Gloria Harris
You can find these books on Amazon.com or your local library may have them for you.
When you see a therapist, include your husband as well. Share that you are working on your issues and that you want to improve not only your situation, but your marriage as well. This should help your husband to see that you are treating the situation as important and that will help your marriage and your anxiety.