Hi Emillie, welcome aboard 
I've moved your thread as you are asking for help, and it's quite a common issue.
When you say advertised on Facebook, do you mean paid advertising (PPC) or simply posting?
I suspect it may be your approach (which a lot of people struggle with). If you look at your facebook page, what do you see? eg:

To me it look like lots of selfpromo, which will be lost in a sea of self promo time lines. Social Media is about being... social. So be sociable and interact. Be the go to Horsebox Bits resource, but do it by helping people. Did you know the best way to recondition a horsebox is by blah blah.
Here is a handy article in how you fit a new tow hitch in 30 minutes, here is a video which shows the best way to fix hinges on your horsebox ramp.
Then in your super duper content, there is a reference where you can buy the replacement parts, or ask for further help, ie your site.
So you are soft selling by engaging, that's how social media works.
It's a different way of selling, which most people get wrong and is a slow process as you establish yourself, credibility and reputation.
If you want direct and instant product sales, then get your website optimised, ranked highly and if need be, reinforce it by Google PPC which is instant and trackable marketing. But this requires budget and expertise, so is dependant on available resources.
Does that help, make sense?