Thanks in advance for any advice.

I've been working for a small steel broker for about 4 years now. I am currently the only female employee, I have the largest work load, but am the lowest paid. My coworkers all earn at least double my earnings. My immiate supervisor spends his day online lining up female escorts -- I know this because he prints out emails he exchanges with these girls & leaves them laying on the printer. He earns a 6 figure salary. I end up having to handle his work load and mine.

The best answer that can be given with the facts available is maybe. If you're the lowest paid because you're female, that's illegal discrimination. If you're the lowest paid because you're the newest, or have the lowest qualifications, or because you didn't negotiate a higher rate at hire and the others did, or because you have less experience, or because the others have a college degree and you don't, or a whole bunch of other reasons, it's not.

Do you and the male employees who earn more than you do, perform the same work? Do you have the same title?

Work load typically doesn't determine pay. Rather, pay typically is based on the duties and responsibilities of the job and the qualifications and skill level necessary to successfully perform the job, plus market factors.

If you think you are underpaid or would like to get a wage increase, you need to discuss that with your supervisor and find out the factors on which pay is based and what is necessary for you to get a wage increase.