Continuing the discussion from Featured Artists vs the rest of us:
Bob, you appear to have a personal facebook account, but not a facebook "Page" for your art. I think looking for facebook "groups" in which to post (alongside many other people) is far less effective than setting up your own page, and here is why.
Currently you have 700 friends(!) but only 69 followers. With only the personal account, you are missing several opportunities:
1. With a Page, you can invitie all of your friends--or a just select number--all at once to "like," and therefore follow, your page. With only a personal account, no one sees your posts unless you "friend" them. Not so with a Page.
2. When one of your friends becomes a follower, there is a link they can use to invite their friends to become followers. (Can't do that with the basic account)
3. Likewise, when someone likes or shares one of your art page's images, many of their friends will see it. Then if the friends' friends' like and share, your likes and shares continue to grow. In this way, you can pick up many "likes" and followers you don't even know--people who like art and may occasionally visit your blog, auctions or gallery and buy something.
4. Finally, if you are so inclined, you can advertise your page and target very specific markets, and you can do it in very small increments. I am not convinced it generates sales, but I tried it for a few days and did pick up about the number of followers they predict for the length and scope of my ad.
I made my FB art page in July, 2014. I don't "work" facebook too hard, because I don't like to spam people with a lot of self promotion. But with only 149 friends (not all of whom give a whit about art) I have 120 followers--many of whom I don't even know--and several friends and followers have bought work they saw there first. I waited a whole year to invite my BIL to my page, doubting he would be very interested, but when he accepted, he shared it, and a whole bunch of his friends also became followers! So you never know.
I have hard-selling acquaintence with many FB friends and followers. She works facebook every day (on both her page and profile) and regularly sells her artwork there. (I "unfollowed" her, because I couldn't take it all.) At least with a page, followers who see your art posts have opted to do so, where as all your "friends" on your personal account might not be as appreciative.
As far as having an "off" week or even month, I think that's bound to happen periodically, for no particular reason. However, if I had to guess what might be a slow time, August (when many people vacation) would top my list. I sold a small piece a couple of weeks ago that the buyer doesn't want me to ship until next week, because she's out of town.