Is this a case of gender/pregnancy discrimination?

I am a Correction Officer at a Prison. The contract between our union and the employer states that: "The employer will make a good faith effort to provide alternative, comparable work and equal pay to a pregnant employee upon a doctor's recommendation." This is in addition to the pregnancy discrimination act of 1978 My doctor has given me a restriction which is no heavy lifting limited to under 50 lbs. which I had to be able to lift at least 50 to get hired. Additionally, they have told me that this is not medical restriction and they are going to continue to place me in my normal work areas. They have threatened me and told me that if I get any other restrictions, (including minimal contact with inmates which such areas do exist) from my doctor that they will force me to leave work on disability pay even though they claim that pregnancy is not a disability. People with similar medical conditions have gotten to participate in a return to work program which places them on light duty or in areas with minimal contact with inmates. They are talking to me in circles what should I do?