In total panic! Unable to get into my site for 3 days-and theme may be corrupted

About a week ago my site suddenly refused to show some images,update plugins, create directories etc. I changed the permissions on the files using an FTP server and everything was then ok.

The next day my site went down for 24 hours then came back on but kept failing to save and making me log back in, then it went off again completely. I checked our host and the stats said our database was full so I arranged to have the size doubled in size.

The next morning I woke up, the database had been expanded but I couldn’t login at all. I have a coming soon page on my site but left this page open to enable login http://www.cercopan.org/why-is-our-work-vital/ The page is just a list without the theme and its calling the page ‘My CMS’ (the name the coming soon plugin automatically assigns before you alter it). When go to login its just taking me to the coming soon page. When i try going though plex on my host I get the same or it gives me a 404 error saying I am forbidden.

I am very much a beginner with website creation and have taught myself as he small charity I work for needed an updated website.I have spent months working full time on it and it was meant to launch this week, so obviously I am very much in a state of panic at the moment! Any help anyone could offer would be most appreciated.