First thing you need to do is get in touch with the contractor that painted your house and Sherwin Williams. Tell both what is happening. Also, take a look around the house for bubbling, peeling and do the nail test. This is to establish the extent of the problem.
Yes it would be best to remove all loose or poorly adhered paint. This layer is the foundation for future layers of paint and a poor foundation produces a poor paint job. Most likely not all the paint on your house is loose. The only way to remove most of the loose paint is with careful use of a pressure washer and hand scraping.