Your SEO could be improved, to help people find your blog.
You need to be promoting 2 angles on social media, to raise awareness of your sale and auction: charity (Age UK) and bargain collectable artwork.
You are offering some amazing opportunities here, which will hopefully raise lots of money for your chosen charity and give people the opportunity to win (because the Secret Postcard Sale is effectively an art lottery as you may or may not buy a collectable piece) some highly collectable artwork. It merits considerably more interest than you are currently receiving! You're auctioning a Philip Treacy hat! :o
Social Media
Get on Twitter, Facebook and Google Plus and promote your 'selling collectable artwork for charity' sale and auction. Tweet and share links to your blog posts (and Ebay auction, when it goes live). Add hashtags to make your tweets/status updates more visible. If you don't have a Twitter account, sign up for one. I think plenty of people will be interested in retweeting about the Treacy hat - add one of your photos to the tweet, a relevant hashtag, a link to the post/auction and a "please #RT".
Keywords & Meta Data
Add some more targeted keywords to your blog articles e.g. "cheap collectable artwork", "charity auction", or whatever you think is most applicable. Try to mention it 2-3 times per post. Remember, the first couple of lines of each blog article are the most important as the first line of your most recent post is the thing glaring at you 'above the fold'. At the moment, the first thing I see above the fold is "a wonderful C4 documentary", which tells me nothing about your great artwork sale and charitable aims.
Tweak your website meta data to be more relevant to search engines. I'm sorry but
Is about as useful as a chocolate teapot. No one is going to be searching for "personal blog about whatever". When was the last time YOU typed that into Google? ;)
Networking
Buddy up with some relevant blogs or websites - perhaps art related - and ask if they'll link to your posts/auction. It's for charity, after all, so people are more likely to be willing to help out.
HTH and GL with your fund-raising! :) xx
PS: If you do get on Twitter, I'm @fcknits and will be happy to retweet for you, anytime - just tag me there and I'll see it in my 'mentions'.