I ran an initial commit of all of my code on 29th January. I've been working on the code on and off and wanted to check in the changes. When I go into my repository in SourceTree all of the files show up in Files in the working tree with + symbols indicating that they are new files. Selecting any of them shows the entire contents of the file from when I checked the files in in January. I've checked the bitbucket website and the files were definitely correctly checked in on the intial checkin. When I try and commit there are no files showing up because SourceTree has decided that nothing has changed.
I haven't used source control a great deal and have run into significant problems with it in the past (including wiping out 2 months worth of work on one occasion) so I don't know how to proceed.