As both a PT and a cyclist....

I would strongly advise against asking a bunch of bikers about medical advice. Just like I would avoid asking your PT about installing a headset.

There may be serious reasonings for not wanting you cycling. If they didnt explain, ask them WHY cycling is bad for your back, at this time.

Sciatica is such a broad term with a variety or sources, your description means nothing. Your PT didnt say stop cycling because of sciatica, but because of your signs and symptoms.

I can have someone in back pain that I want to get on a bike, and someone who I definitely DO NOT want on a bike at all.

Summary:
Talk to your PT.
Dont listen to people on message boards.