Good question. There are several ways to determine where your fees fall. If there's an industry association, that's a good place to find out the range of fees in your area. Your local chamber of commerce may have access to this type of information. If you know others in your industry, you can have a conversation with the intent of wanting to make sure you don't undercut them. This is always a delicate conversation because you do not want to give the appearance of price fixing. 

At all times, you are asking for a range. Additionally, it sounds as if you may not be comfortable raising your fees. When you have confidence in the worth of your services, you are not afraid to charge a worthy fee.  Are you sure you are offering the best value? Is there an area you can improve? When you can answer these questions confidently, you will know the appropriate amount to charge.