Frustrating, but it seems to me that unless you select the option in iCloud preference to synchronise ALL your photos and videos then it won't give a photo stream, which for me means paying £'s per month for something I don't otherwise need. I have Crashplan, doesn't just backup photo's and video's but the entire Mac for a fraction of the cost, and historic, and incremental.
I only wanted to use it as was before, I take a photo, I don't need to plug in, I just go to Photostream and there they all are. Not any more it seems.
I can't prove this as I can't turn on sync all photos without paying, either that are I destroy my library and downsize it. I suppose I could run it on a different account to test. Meanwhile, it's back to using cable to import photos 🙁