Hard drive issue

I first noticed that when a USB Flash drive (32gb) was empty but Get info showed it had 28gb used. And I couldn't add any files. I reformatted the drive and the problem cleared. Then minutes later my Time Machine allocated drive (Samsung 1TB Hard Drive) stated the back couldn't complete back up because I have no space. Looked on the Get Info and had few hundred MB left. When I know all that is on this drive adds to about 200GB! I really dont want to reformat this drive too.

Any Ideas why this is happening and how can I stop it? I really dont want my internal HDD to do the same!

PLEASE HELP!

Actually, still emptying trash now. Deleted all old back up files and that seems to have caused the issue.
Thanks for the help