You're thinking about this the wrong way; if do not have a topic you want to write about - then don't write.
I'm not being flippant: You should write and publish something if you feel it's important to express in writing and to disseminate. Don't try to produce publications for publication's sake.
But maybe it's the other way around: You're frustrated about being so passive - like you said, just "reading, reading, reading" - rather than producing something written. Well, in that case, instead of thinking about what to write, think about what you want to know or figure out. What questions about human society (be it history, sociology, psychology or whatever you're focused on) intrigue you?
When you have your questions, you look for what's already been written or said. If it's sufficient - then you had an interesting read and can perhaps put the knowledge to some use; and if there isn't a definite answer to your question - that's what you can contemplate, explore, study, and eventually publish about yourself.
Edit: I gave a general answer, but your tags suggest you are in grad school. If that's the case, then also consider:
- You have an advisor. Talk to him/her about this - that's what s/he's there for.
- If you've submitted a research proposal, then you've asked yourself some of these research questions already. Are you actually looking into them? Do you have satisfying answers to them?