Since you are having you monthly period, it means that you are definitely not pregnant.
The back ache / sciatica that you are experiencing at the moment may be caused by other factors. A chiropractor may be able to help you with this concern.
The nerve (the sciatic) goes to the muscles that move the leg. If the "pinching" is removed by opening the foramen (Foraminal Stenosis) that the nerve goes through, the ability to walk will come back.
I believe that this could be siatica.<---- spelling could be wrong... but I have the same pain from time to time and it's very painful. Could be related to low back issues or stress. Elevating your legs at leisure times or putting a pillow between your legs when you sleep can help. I'm not a medical person, but I know a lot about this issue. Ask your doctor about this if it persists or gets worse. Hope this helps.