Asking for a raise is a gut wrenching experience and by all accounts, most people never make such a request because they don't know how to approach the subject with their bosses. Most people are nervous and reluctant, and that is understandable. But if you don't ask for a raise, your employer isn't going to volunteer it.
If you don't ask, you may never get the higher income that you deserve. You have to prepare yourself to stand up and ask for the raise. You have to be reasonable with your request but never undervalue the work you do on your job.