Your site is probably new, until your site ages and matures you can expect your SERPs to change. It is not uncommon for newer sites to see SERP fluctuations for the first 4-6 months.
SERP fluctuations are sometimes due to change in algo, backlinks, keywords optimization and so many factors that is hard to define one by one. Google only knows. You just need to be patient and work hard on optimizing the keywords of your site.
On-Page and Off-Page Optimization On Page--- -Make sure your keyword(s) are present throughout all your pages -Meta Tags Off-Page -BACKLINKS!!!!!!!!
when creating a link page does it have to be visible to visitors ? (i.e in the menu bar or bottom of page) or can it simply be on the site somewhere but not published ? how does that influence ranking ?
my sites fluctuate in the rankings all the time. The ones with more backlinks and that are older tend to be more stable.