You can do a trademark search at
United States Patent and Trademark Office (click on the Search Marks link under Trademarks). You will want to check whether the mark is live (i.e., someone is actively using it and they are paying the trademark fees) and the category for which it was registered. There is one called Pretty Boy Clothing specifically. If someone is using the term Pretty Boy for clothing - you can't use the name for your clothing items. So, you'll have to pick a different name.