Indiana Lawyer? I work in a department with 3 women and we don't all get paid the same...?

I have been working in a "service" department with the same three women for almost 5 years, the first one has been here about 8 to 10 years, the second has been here about 6 months longer then I have, but the first makes $10 and hour, the second $9.50 and hour and then me, i make $7.50 an hour, we all do the same exact work, and work full time, we all have the same amount of experience and i would think we, by law, doing the same job should get equal pay, besides the one that of course has more years in the company.. I have tried to read on the the state law of equal pay, but it just seems like they are saying if it's a women doing the same job as a man then it would qualify, so would my situation fall under anything?? am i, under the part of "un" equal or is what they are doing considered equal..?? can someone help.. HIGHLAND , INDIANA