SEVERE SCIATIC PAIN

Em
Ok so I have PRE existing sciatic pains, and being pregnant has escalated them to the max. I have literally peed myself because it takes so long to move one foot infront of the other, walking from my couch to my toilet at the end of the day. 
So my question is, can I get a doctor's note excusing me from certain activities at work?  I work for a rental car company and a large part of my job includes cleaning vehicles (bending, vacuuming, scrubbing etc).
Can I get a note excusing me from the cleaning part of my job, because I'm in SO much pain during, and after work?